Scaffolds formed from polymer-protein conjugates, methods of generating same and uses thereof

ABSTRACT

Conjugates are provided herein which comprise a protein attached to at least two polymeric moieties, at least one of which exhibits reverse thermal gelation. The conjugates are suitable for being cross-linked by non-covalent and/or covalent cross-linking. Compositions-of-matter comprising cross-linked conjugates are provided herein, as well as processes for producing same. Methods of controlling a physical property of compositions-of-matter are also provided herein. The conjugates and compositions-of-matter may be used for various applications, such as cell growth, tissue formation, and treatment of disorders characterized by tissue damage or loss, as described herein.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/515,298 filed on Jun. 12, 2012, which is a National Phase of PCTPatent Application No. PCT/IL2010/001072 having International filingdate of Dec. 16, 2010, which claims the benefit of priority under 35 USC§119(e) of U.S. Provisional Patent Application No. 61/282,104 filed onDec. 16, 2009. The contents of the above applications are allincorporated by reference as if fully set forth herein in theirentirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates topolymer-protein conjugates and, more particularly, but not exclusively,to polymer-protein conjugates which form a scaffold, to processes ofgenerating same and to uses thereof in, for example, tissue engineering.

As the field of tissue engineering evolves, there is a need for newbiomaterial scaffolds that can provide more than just architectural andmechanical support. New “hybrid” materials are being developed assophisticated scaffolds wherein biological polymers such as alginate,collagen or fibrinogen are combined with synthetic polymers to provideadded versatility and bioactivity at the material/cell interface. Fromthe perspective of cellular interactions, the biological domains of thehybrid material may actively participate in stimulating cells towardsthe formation of functional tissues. Bioactive signals are controlledvia biological macromolecules such as protein segments [Cutler andGarcia, Biomaterials 2003, 24:1759-1770], growth factors [Seliktar etal., J Biomed Mater Res A 2004, 68:704-716; Zisch et al., FASEB J 2003;17:2260-2262; DeLong et al., Biomaterials 2005, 26:3227-3234] or shortbioactive peptides [Mann et al., Biomaterials 2001, 22:3045-3051; Lutolfet al., Proc Natl Acad Sci USA 2003, 100:5413-5418; Stile and Healy,Biomacromolecules 2001, 2:185-194]. These elements are capable ofinfluencing cell migration, proliferation, and guided differentiation[Dikovsky et al., Biomaterials 2006, 27:1496-1506]. From the perspectiveof biomaterial properties, “smart” polymers may also be used to providebetter control over bulk features of the scaffold in response to changesin temperature, pH, or light [Furth et al., Biomaterials 2007,28:5068-5073; Galaev and Mattiasson, Trends Biotechnol 1999,17:335-340]. Hybrid materials made with smart polymers have additionaldegrees of freedom, including control over bulk density, degradability,porosity and compliance, all of which can be regulated by the syntheticpolymer component [Peppas et al., Annu Rev Biomed Eng 2000, 2:9-29;Tsang and Bhatia, Adv Drug Deliv Rev 2004, 56:1635-1647; 3] Baier Leachet al., Biotechnol Bioeng 2003, 82:578-589].

Hybrid materials have been prepared based on conjugation of endogenousproteins with versatile synthetic polymers [Almany and Seliktar,Biomaterials 2005, 26:2467-2477; Gonen-Wadmany et al., Biomaterials2007, 28:3876-3886; Peled et al., Biomed Mater Res A 2007, 80:874-884;Seliktar, Ann NY Acad Sci 2005, 1047:386-394]. The effect of alternatingstructural properties of hydrogels made from poly(ethylene glycol) (PEG)conjugated to fibrinogen on the morphology and remodeling ofencapsulated smooth muscle cells has been investigated [Dikovsky et al.,Biomaterials 2006, 27:1496-1506; Dikovsky et al., Biophys J 2008,94:2914-2925]. These materials exhibited an ability to control cellularbehavior by changing factors such as density, stiffness, and proteolyticdegradability through the versatile synthetic component. The fibrinogenis a natural substrate for tissue remodeling which contains several cellsignaling domains, including a protease degradation substrate and celladhesion motifs [Herrick et al., Int J Biochem Cell Biol 1999,31:741-746; Werb, Cell 1997, 91:439-442].

International Patent Application PCT/IL2004/001136 (published asWO2005/061018) and U.S. patent application Ser. No. 11/472,437 describea biodegradable scaffold composed of a protein (e.g., fibrinogen)backbone cross-linked by a synthetic polymer such as poly(ethyleneglycol), and methods of generating such scaffolds from polymer-proteinconjugates.

International Patent Application PCT/IL2008/000521 (published as WO2008/126092) describes scaffolds composed of albumin or thiolatedcollagen cross-linked by a synthetic polymer such as poly(ethyleneglycol).

Reverse thermo-responsive polymers are capable of producing lowviscosity aqueous solutions at ambient temperature, and forming a gel ata higher temperature. This property may be used to generate implants insitu [Cohn et al., Biomacromolecules 2005, 6:1168-1175].

Stile and Healy [Biomacromolecules 2001, 2:185-194] modified a smartpolymer, N-isopropylacrylamide, with RGD (Arg-Gly-Asp) containingpeptides to form a reversible thermo-sensitive hydrogel with bioactivesegments for cell culture studies. They reported that the conjugation ofRGD peptides to the thermo-responsive smart polymer does not compromisethe temperature-induced sol-gel transition of the hydrogels. Theyfurther reported that the conjugated RGD peptide enhanced the biologicalinteractions of the otherwise inert N-isopropylacrylamide polymernetwork.

Reverse thermo-responsive polymers having a poly(ethylene oxide)(PEO)-poly(propylene oxide) (PPO)-PEO tri-block structure, referred toas “poloxamers”, have also been reported. The endothermic sol-geltransition takes place due to an increase in entropy caused by releaseof water molecules bound to the PPO segments as temperature increases[Alexandridis, Colloid Surface A 1995, 96:1-46].

Pluronic® F127 poloxamer is a well known synthetic triblock copolymer(PEO₉₉-PPO₆₇-PEO₉₉) [Nagarajan and Ganesh, J Colloid Interface Sci 1996,184:489-499; Sharma and Bhatia, Int J Pharm 2004, 278:361-377; Cohn etal., Biomaterials 2003, 24:3707-3714], that exhibits a reverse thermalgelation (RTG) property above a critical temperature in aqueoussolutions. Cohn et al. [Polym Adv Tech 2007; 18:731-736] reported thatpolymerized F127 displays reverse thermal gelation at lowerconcentrations and with enhanced mechanical properties, as compared withF127.

Additional background art includes Halstenberg et al. [Biomacromolecules2002, 3:710-723], Cohn et al. [Polym Adv Tech 2007; 18:731-736], andU.S. Pat. No. 7,842,667.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a conjugate comprising a polypeptide having attachedthereto at least two polymeric moieties, at least one of the polymericmoieties exhibiting a reverse thermal gelation.

According to an aspect of some embodiments of the present inventionthere is provided a composition-of-matter comprising a cross-linked formof a conjugate described herein, the cross-linked form comprising aplurality of molecules of the conjugate cross-linked to one another.

According to an aspect of some embodiments of the present inventionthere is provided a process of producing a composition-of-matterdescribed herein, the process comprising heating a solution of aplurality of molecules of a conjugate described herein from a firsttemperature to a second temperature, the second temperature being suchthat a reverse thermal gelation of the conjugate in the solution iseffected, thereby producing the composition-of-matter.

According to an aspect of some embodiments of the present inventionthere is provided a process of producing a composition-of-matterdescribed herein, the process comprising subjecting a solutioncomprising a plurality of molecules of a conjugate described herein, theconjugate comprising at least one cross-linking moiety, to conditionsthat effect covalent cross-linking of the cross-linking moieties,thereby producing the composition-of-matter.

According to an aspect of some embodiments of the present inventionthere is provided a process of producing a composition-of-matterdescribed herein in vivo, the process comprising:

(a) subjecting a solution comprising a plurality of molecules of aconjugate described herein, the conjugate comprising at least onecross-linking moiety, to conditions that effect covalent cross-linkingex vivo, to thereby produce a covalently cross-linked scaffold; and

(b) subjecting the covalently cross-linked scaffold to a physiologicaltemperature in vivo, such that a reverse thermal gelation of thescaffold is effected in vivo, thereby producing thecomposition-of-matter.

According to an aspect of some embodiments of the present inventionthere is provided a method of controlling a physical property of acomposition-of-matter described herein, the method comprisingcontrolling a parameter selected from the group consisting of aconcentration of a conjugate described herein in solution, an ambienttemperature, a presence or absence of an initiator, a dose ofirradiation during covalent cross-linking, and a cross-linkingtemperature.

According to an aspect of some embodiments of the present inventionthere is provided a process of producing the conjugate described herein,the process comprising covalently attaching a polymer to a polypeptide,the polymer and the polypeptide being such that at least two polymermolecules covalently attach to a molecule of the polypeptide, wherein atleast one of the two polymer molecules exhibits a reverse thermalgelation, thereby producing the conjugate.

According to an aspect of some embodiments of the present inventionthere is provided a use of a conjugate described herein or of acomposition-of-matter described herein in the manufacture of amedicament for repairing tissue damage.

According to an aspect of some embodiments of the present inventionthere is provided a use of a conjugate described herein or of acomposition-of-matter described herein in the manufacture of amedicament for treating a subject having a disorder characterized bytissue damage or loss.

According to an aspect of some embodiments of the present inventionthere is provided a method of inducing formation of a tissue in vivo,the method comprising implanting a composition-of-matter describedherein in a subject, to thereby induce the formation of the tissue.

According to an aspect of some embodiments of the present inventionthere is provided a method of inducing formation of a tissue in vivo,the method comprising implanting a plurality of molecules of a conjugatedescribed herein in a subject, to thereby induce the formation of thetissue.

According to an aspect of some embodiments of the present inventionthere is provided a method of inducing formation of a tissue ex vivo,the method comprising subjecting a composition-of-matter which comprisescells, as described herein, to conditions conductive to growth of thecells, to thereby induce tissue formation.

According to an aspect of some embodiments of the present inventionthere is provided a method of treating a subject having a disordercharacterized by tissue damage or loss, the method comprising implantinga composition-of-matter described herein in a subject, to thereby induceformation of the tissue, thereby treating the disorder characterized bytissue damage or loss.

According to an aspect of some embodiments of the present inventionthere is provided a method of treating a subject having a disordercharacterized by tissue damage or loss, the method comprising implantinga plurality of molecules of a conjugate described herein in a subject,to thereby induce formation of the tissue, thereby treating the disordercharacterized by tissue damage or loss.

According to an aspect of some embodiments of the present inventionthere is provided a pharmaceutical, cosmetic or cosmeceuticalcomposition comprising a plurality of molecules of a conjugate describedherein, the composition being identified for use in inducing formationof a tissue upon being contacted with a tissue and further uponsubjecting the composition to a physiological temperature.

According to an aspect of some embodiments of the present inventionthere is provided a kit for inducing formation of a tissue, the kitcomprising:

(a) a conjugate described herein;

(b) an aqueous solvent; and

(c) instructions for cross-linking an aqueous solution the conjugate inorder to form a scaffold for inducing formation of the tissue.

According to some embodiments of the invention, each of the polymericmoieties exhibits a reverse thermal gelation.

According to some embodiments of the invention, at least one of thepolymeric moieties further comprises at least one cross-linking moietyfor covalently cross-linking a plurality of molecules of the conjugateto one another.

According to some embodiments of the invention, the conjugate is of thegeneral formula:

X(—Y—Zm)n

wherein:

X is a polypeptide described herein;

Y is a polymeric moiety described herein;

Z is a cross-linking moiety described herein;

n is an integer greater than 1; and

m is 0, 1 or an integer greater than 1.

According to some embodiments of the invention, the polypeptidecomprises a protein or a fragment thereof.

According to some embodiments of the invention, the protein is selectedfrom the group consisting of a cell signaling protein, an extracellularmatrix protein, a cell adhesion protein, a growth factor, protein A, aprotease, and a protease substrate.

According to some embodiments of the invention, the extracellular matrixprotein is selected from the group consisting of fibrinogen, collagen,fibronectin, elastin, fibrillin, fibulin, vimentin, laminin and gelatin.

According to some embodiments of the invention, the polypeptidecomprises a fibrinogen or a fragment thereof.

According to some embodiments of the invention, the protein isdenatured.

According to some embodiments of the invention, the polypeptide is adenatured fibrinogen.

According to some embodiments of the invention, the polymeric moietycomprises a synthetic polymer.

According to some embodiments of the invention, at least one of thepolymeric moieties comprises a poloxamer (poly(ethylene oxide-propyleneoxide) copolymer).

According to some embodiments of the invention, each of the polymericmoieties comprises a poloxamer.

According to some embodiments of the invention, the poloxamer is F127poloxamer.

According to some embodiments of the invention, at least one of thepolymeric moieties comprises T1307 polymer.

According to some embodiments of the invention, the polymeric moietiesare selected from the group consisting of a Pluronic® polymer and aTetronic® polymer.

According to some embodiments of the invention, each of the polymericmoieties comprises from 1 to 10 of the cross linking moieties.

According to some embodiments of the invention, the cross-linking moietycomprises a polymerizable group.

According to some embodiments of the invention, the polymerizable groupis polymerizable by free radical polymerization.

According to some embodiments of the invention, the polymerizable groupis selected from the group consisting of an acrylate, a methacrylate, anacrylamide, a methacrylamide, and a vinyl sulfone.

According to some embodiments of the invention, the polypeptide isdenaturated fibrinogen and the polymeric moieties comprise F127poloxamer.

According to some embodiments of the invention, the conjugate comprisesF127 poloxamer diacrylate moieties, wherein an acrylate group of each ofthe F127 poloxamer diacrylate moieties is attached to a cysteine residueof the fibrinogen.

According to some embodiments of the invention, the polypeptide isdenaturated fibrinogen and the polymeric moieties comprise T1307polymer.

According to some embodiments of the invention, the conjugate comprisesT1307 tetraacrylate moieties, wherein an acrylate group of each of theT1307 tetraacrylate moieties is attached to a cysteine residue of thefibrinogen.

According to some embodiments of the invention, the conjugate ischaracterized by an ability to undergo reverse thermal gelation in anaqueous solution.

According to some embodiments of the invention, the reverse thermalgelation is effected at a concentration of less than 10 weight percentsof the conjugate in the aqueous solution.

According to some embodiments of the invention, the reverse thermalgelation of the conjugate increases a shear storage modulus of theaqueous solution by at least ten-folds.

According to some embodiments of the invention, the reverse thermalgelation increases a shear storage modulus of the aqueous solution to atleast 20 Pa.

According to some embodiments of the invention, the reverse thermalgelation increases a shear storage modulus of the aqueous solution fromless than 2 Pa to at least 20 Pa.

According to some embodiments of the invention, the reverse thermalgelation occurs upon an increase of temperature from 10° C. to 55° C.

According to some embodiments of the invention, the reverse thermalgelation is reversible.

According to some embodiments of the invention, the reverse thermalgelation forms a biodegradable gel.

According to some embodiments of the invention, the conjugate isidentified for use in generating a scaffold.

According to some embodiments of the invention, the conjugate isidentified for use in reversibly generating a scaffold.

According to some embodiments of the invention, the scaffold is ahydrogel.

According to some embodiments of the invention, the hydrogel ischaracterized by a shear storage modulus of at least 15 Pa at atemperature of 37° C.

According to some embodiments of the invention, the hydrogel is capableof undergoing a reverse thermal gelation.

According to some embodiments of the invention, thecomposition-of-matter is a hydrogel.

According to some embodiments of the invention, thecomposition-of-matter is generated by a reverse thermal gelation of theplurality of molecules of the conjugate in an aqueous solution.

According to some embodiments of the invention, the plurality ofmolecules of the conjugate are non-covalently cross-linked to oneanother.

According to some embodiments of the invention, the cross-linked form ofthe conjugate is reversible.

According to some embodiments of the invention, at least one of thepolymeric moieties comprises a cross-linking moiety, and the pluralityof molecules of the conjugate are covalently cross-linked to oneanother.

According to some embodiments of the invention, thecomposition-of-matter is generated by subjecting a plurality ofmolecules of the conjugate to conditions for effecting cross-linking ofthe cross-linking moieties.

According to some embodiments of the invention, thecomposition-of-matter is characterized by a shear storage modulus of atleast 20 Pa at a temperature of 37° C.

According to some embodiments of the invention, thecomposition-of-matter is capable of undergoing a reverse thermalgelation.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter increases a shear storage modulusof the composition-of-matter by at least 200%.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter increases a shear storage modulusof the composition-of-matter to at least 15 Pa.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter increases a shear storage modulusof the composition-of-matter from a first value in a range of from 0.5Pa to 200 Pa to a second value which is at least 20% higher than thefirst value.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter increases a shear storage modulusof the composition-of-matter from a first value to a second value in arange of from 20 Pa to 5000 Pa, the second value being at least 20%higher than the first value.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter occurs upon an increase oftemperature from 10° C. to 55° C.

According to some embodiments of the invention, the reverse thermalgelation of the composition-of-matter is reversible.

According to some embodiments of the invention, thecomposition-of-matter is characterized by a shear storage modulus of oneportion of the composition-of-matter that is different from a shearstorage modulus of at least one other portion of thecomposition-of-matter.

According to some embodiments of the invention, thecomposition-of-matter is biodegradable.

According to some embodiments of the invention, thecomposition-of-matter further comprises cells therein.

According to some embodiments of the invention, thecomposition-of-matter is identified for use in inducing a formation of atissue.

According to some embodiments of the invention, thecomposition-of-matter is identified for use in repairing tissue damage.

According to some embodiments of the invention, thecomposition-of-matter is produced in vivo.

According to some embodiments of the invention, the abovementionedsecond temperature is a physiological temperature.

According to some embodiments of the invention, the conjugate comprisesat least one polymeric moiety that further comprises at least onecross-linking moiety, and the process further comprises subjecting thesolution to conditions that effect cross-linking of the cross-linkingmoieties.

According to some embodiments of the invention, subjecting the solutionto the conditions that effect cross-linking is effected prior to theheating.

According to some embodiments of the invention, subjecting the solutionto the conditions that effect cross-linking is effected subsequent tothe heating.

According to some embodiments of the invention, the covalentcross-linking is effected in vivo.

According to some embodiments of the invention, the covalentcross-linking is effected ex vivo, to thereby produce a covalentlycross-linked scaffold, and the process further comprises subjecting thecovalently cross-linked scaffold to a physiological temperature in vivo,such that a reverse thermal gelation of the scaffold is effected invivo, thereby producing a composition-of-matter described herein.

According to some embodiments of the invention, the conditions compriseirradiation.

According to some embodiments of the invention, the conditions comprisea presence of a free radical initiator.

According to some embodiments of the invention, the solution furthercomprises cells, and the process is for producing acomposition-of-matter comprising cells embedded therein.

According to some embodiments of the invention, the conjugate comprisesat least one cross-linking moiety, and the method further comprisescovalently cross-linking the plurality of molecules of the conjugate.

According to some embodiments of the invention, the cross-linking iseffected by subjecting the plurality of molecules of the conjugate toconditions that effect covalent cross-linking of the cross-linkingmoiety.

According to some embodiments of the invention, the conjugate comprisesat least one cross-linking moiety, and the composition described hereinis identified for use in inducing formation of a tissue upon furthersubjecting the plurality of molecules of the conjugate to conditionsthat effect covalent cross-linking of the cross-linking moiety.

According to some embodiments of the invention, a pharmaceutical,cosmetic or cosmeceutical composition described herein further comprisesan initiator for inducing covalent cross-linking of the cross-linkingmoiety.

According to some embodiments of the invention, a pharmaceutical,cosmetic or cosmeceutical composition described herein is packaged in apackaging material and identified in print, in or on the packagingmaterial, for use in inducing formation of the tissue.

According to some embodiments of the invention, the conjugate comprisesat least one cross-linking moiety, and the kit further comprises aninitiator for inducing covalent cross-linking of the cross-linkingmoiety.

According to some embodiments of the invention, the kit furthercomprises cells for embedding in the scaffold described herein.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIGS. 1A and 1B are schemes showing the synthesis of F127 poloxamerdiacrylate (FIG. 1A) from F127 poloxamer and acryloyl chloride in a 1:2mixture of dichloromethane (DCM) and toluene with triethylamine ((ET)₃N)at room temperature (R.T.), and the synthesis of an F127poloxamer-fibrinogen conjugate (FF127) using the poloxamer diacrylate(FIG. 1B) in phosphate buffer saline (PBS) with 8 M urea, according tosome embodiments of the invention;

FIG. 2 presents comparative plots showing the storage modulus (G′) ofFF127 solutions at fibrinogen concentrations of 4, 6 and 8 mg/ml, as afunction of temperature; the inset graph shows the storage modulus (G′)and loss modulus (G″) of an FF127 solution with 8 mg/ml fibrinogen;

FIGS. 3A and 3B present graphs showing the storage moduli of FF127solutions with (FIG. 3B) and without (FIG. 3A) chemical (covalent)cross-linking of the FF127, as a function of time with cyclictemperature changes between 15° C. and 37° C., in the presence of 0.1 or0.01 mg/ml collagenase, and in the absence of collagenase;

FIG. 4 is a schematic illustration of fibrinogen polypeptides (red,green and blue) conjugated to a polymer (black) and hydrogel assemblyaccording to some embodiments of the invention by reversible(non-covalent) cross-linking of the polymer in a temperature-dependentmanner or irreversible UV-induced (covalent) cross-linking;

FIG. 5 is a graph showing a reversible increase in storage modulus (G′)of an FF127 solution by increasing the ambient temperature (T_(amb)) anda subsequent irreversible UV-induced increase of the storage modulus;

FIG. 6 presents comparative plots showing the storage modulus (G′) of achemically (covalently) cross-linked FF127 at fibrinogen concentrationsof 4, 6 and 8 mg/ml, as a function of temperature; the inset graph showsthe storage modulus (G′) and loss modulus (G″) of a chemically(covalently) cross-linked FF127 with 8 mg/ml fibrinogen;

FIGS. 7A and 7B present graphs showing the effect of oscillatory stressand temperature changes on the storage modulus (G′; FIG. 7A) and lossmodulus (G″; FIG. 7B) of hydrogels of 8 mg/ml FF127 with (black line)and without (dotted line) chemical (covalent) cross-linking(temperatures were cycled between 37° C. (red lines) and 15° C. (bluelines) at a rate of 1° C./second; oscillation frequency was 1 Hz; strainwas 2%);

FIG. 8 presents a graph showing the storage modulus (G′) of FF127hydrogels (8 mg/ml fibrinogen) cross-linked (covalently) by applicationof UV light at different cross-linking temperatures (T_(cl)), followingexposure to ambient temperatures (T_(amb)) (before T_(amb)=37° C.,T_(amb)=T_(cl));

FIG. 9 is a bar graph showing the swelling ratio of FF127 hydrogels (6mg/ml fibrinogen) formed with cross-linking temperatures (T_(cl)) of 21°C. or 37° C. and a hydrogel formed from cross-linked 12 kDaPEG-fibrinogen conjugates (PF12 kDa), at ambient temperatures (T_(amb))of 4° C. and 37° C.;

FIGS. 10A and 10B are images showing the diameters (marked by blackcircles) of FF127 hydrogels (6 mg/ml fibrinogen) chemically (covalently)cross-linked at a temperature of 21° C. (FIG. 10A) or 37° C. (FIG. 10B),and then subjected to ambient temperatures of 37° C.; images on leftshow the hydrogels at the cross-linking temperature immediately afterchemical cross-linking, and images on right show the chemically(covalently) cross-linked hydrogels after incubation at 37° C.;

FIG. 11 presents comparative plots showing the degradation in trypsinsolution of hydrogels formed by cross-linking FF127 or 12 kDaPEG-fibrinogen conjugate (PF12) at a cross-linking temperature (T_(cl))of 21° C. or 37° C. (storage moduli (G′) and degradation half-lives(t50) of the hydrogels are indicated);

FIG. 12 is a bar graph showing the storage modulus (G′) of hydrogelsformed by cross-linking FF127 (at a cross-linking temperature (T_(cl))of 21° C. or 37° C.), 12 kDa PEG-fibrinogen conjugate (PF12 kDa), orF127 diacrylate (F127-DA), at an ambient temperature (T_(amb)) of 37°C.;

FIGS. 13A and 13B are schemes illustrating the synthesis (FIG. 13A) of aT1307-fibrinopeptide conjugate (FT-1307) in phosphate buffer saline(PBS) with 8 M urea at room temperature (R.T.), and the structure of theconjugate (FIG. 13B), according to some embodiments of the invention;

FIGS. 14A and 14B present comparative plots (FIG. 14A) and a bar graph(FIG. 14B) showing the storage modulus (G′) of FT-1307 (6 mg/mlfibrinogen) hydrogels cross-linked at a temperature (T_(cl)) of 4° C.,21° C. or 37° C., as a function of ambient temperature (FIG. 14A), andas a mean±SEM of 4 samples at an ambient temperature of 37° C. (FIG.14B);

FIG. 15 is a bar graph showing the swelling ratio (Q_(M)) of FT1307hydrogels (6 mg/ml fibrinogen) cross-linked at a temperature (T_(cl)) of4° C., 21° C. or 37° C., at an ambient temperature (T_(amb)) of 4° C.and 37° C.;

FIG. 16 is a bar graph showing the biodegradation half-life (T₁₁₂) intrypsin solution of FT1307 hydrogels (6 mg/ml fibrinogen) cross-linkedat a temperature (T_(cl)) of 4° C., 21° C. or 37° C.;

FIG. 17 presents images showing human foreskin fibroblasts seeded inhydrogels formed by cross-linking FF127 (at a cross-linking temperature(T_(cl)) of 21° C. or 37° C.), 12 kDa PEG-fibrinogen conjugate (PEG-Fib12 kDa), or F127 diacrylate (F127-DA), 3 and 6 days after seeding (scalebar=100 μm);

FIG. 18 is an image showing human foreskin fibroblasts seeded in FF127hydrogels with (Physical+Chemical) and without (Physical) chemicalcross-linking of the FF127 (at a cross-linking temperature of 37° C.), 3and 6 days after seeding (scale bar=100 μm);

FIG. 19 is a graph showing the viability of human foreskin fibroblastsseeded for 0 or 3 days in hydrogels formed by cross-linking FF127 at across-linking temperature (T_(cl)) of 21° C. or 37° C. (storage moduli(G′) and degradation half-lives (t50) of the hydrogels are indicated);

FIGS. 20A and 20B are an image (FIG. 20A) and a graph (FIG. 20B) showingthe cellular invasion from smooth muscle tissue into hydrogels formed bycross-linking FF127 (at a cross-linking temperature (T_(cl)) of 21° C.or 37° C.) or 12 kDa PEG-fibrinogen conjugate (PF12 kDa), on days 1, 3and 5 after encapsulation of the tissue in the hydrogel; FIG. 20B showsthe invasion distance as a function of time (scale bar=100 μm);

FIG. 21 is an image showing human foreskin fibroblasts 3 hours, 3 daysor 6 days after being seeded in FT1307 hydrogels with storage moduli of52, 244 or 373 Pa (viable cells are stained with calcein (green) and nonviable cells are stained with ethidium (orange); scale bar=100 μm);

FIG. 22 is an image showing HeLa cells 3 hours, 3 days or 6 days afterbeing seeded in FT1307 hydrogels with storage moduli of 52, 244 or 373Pa (viable cells are stained with calcein (green) and non viable cellsare stained with ethidium (orange); scale bar=100 μm);

FIGS. 23A and 23B depict the preparation of a cell-seeded FF127 capsuleembedded in an FT1307 hydrogel, according to some embodiments of theinvention;

FIGS. 24A and 24B are photographs showing an FF127 capsule (6 mg/mlfibrinogen) seeded with human foreskin fibroblasts (green) embedded for6 days in an FT1307 hydrogel (6 mg/ml fibrinogen) having a storagemodulus of 373 Pa (FIG. 24A) or 52 Pa (FIG. 24B) (scale bar=200 μm);

FIGS. 25A and 25B are photographs showing an FF127 capsule (6 mg/mlfibrinogen) seeded with Hela cells (green) embedded for 6 days in anFT1307 hydrogel (6 mg/ml fibrinogen) having a storage modulus of 373 Pa(FIG. 25A) or 52 Pa (FIG. 25B) (scale bar=200 μm);

FIGS. 26A and 26B are photographs showing FF127 capsules (6 mg/mlfibrinogen) seeded with a co-culture of human foreskin fibroblasts(stained green) and Hela cells (stained red) on day 0 (FIG. 26A) and onday 5 (FIG. 26B) of being embedded in an FT1307 hydrogel (6 mg/mlfibrinogen) (dashed circles in FIG. 26B show the diameter of the cellculture on day 0, scale bar=200 μm); and

FIGS. 27A and 27B are photographs showing FF127 capsules (6 mg/mlfibrinogen) seeded with a co-culture of human foreskin fibroblasts(stained green) and Hela cells (stained red) on day 0 (FIG. 26A) and onday 5 (FIG. 26B) of being embedded in an FT1307 hydrogel (6 mg/mlfibrinogen) (scale bar=200 μm).

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates topolymer-protein conjugates and, more particularly, but not exclusively,to polymer-protein conjugates which form a scaffold, to processes ofgenerating same and to uses thereof in, for example, tissue engineering.

The conjugation of a synthetic polymer to a natural protein such asfibrinogen provides a means of creating biocompatible hydrogels whilecontrolling their physical properties. The conjugation reaction isintended to endow the protein constituent with additional structuralversatility, without compromising its biocompatibility.

The present inventors have previously disclosed a methodology ofgenerating hydrogels made from a synthetic polymer such as poly(ethyleneglycol) (PEG) conjugated to fibrinogen, which enables to controlcellular behavior of the formed hydrogels by manipulating factors suchas density, stiffness, and proteolytic degradability through theversatile synthetic component.

In a search for methodologies for generating hydrogels with improvedcontrol of the hydrogel's characteristics, the present inventors havedesigned and successfully practiced a methodology of generating “smart”hydrogels, by conjugating to proteins a synthetic polymer that exhibitsa reverse thermal gelation (RTG) property above a critical temperaturein aqueous solutions.

This methodology was found to produce hydrogels with an exceptionalcontrol of physical characteristics of the hydrogels, since it allowsmanipulating these characteristics by selecting, for example, the degreeand nature of the cross-linking reactions that lead to gel formation.Since it was uncovered that the protein-polymer conjugates exhibit areverse thermal gelation property, the degree and occurrence ofnon-covalent (physical) cross-linking can be controlled, wherebychemical conditions can be selected for effecting covalent cross-linkingif desired.

Thus, using a combination of photo-polymerization cross-linking andtemperature, an exceptional control over physical properties of thegenerated hydrogels was demonstrated. The ability of the generatedhydrogels to act as a matrix for cell and tissue growth and survival(e.g., as a scaffold) has also been demonstrated.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details set forth in the following description orexemplified by the Examples. The invention is capable of otherembodiments or of being practiced or carried out in various ways.

The present inventors have demonstrated the novel methodology whileutilizing Pluronic® F127 poloxamer and Tetronic® T1307 copolymer (apoloxamer derivative) which are end-functionalized with acryl groups andare reacted with denatured fibrinogen via a Michael-type additionreaction to form a protein-copolymer conjugate. These exemplarypolymeric conjugates could cross-link to form a structure comprisingmultiple units (“unimers”) of the conjugate. Rheological measurementswere conducted on the functionalized unimers and the hydrogels generatedtherefrom in order to characterize the physical response of theseconjugates to environmental stimuli (e.g., temperature responsiveness).

The present inventors have thus further uncovered that the generatedhydrogels retain the biocompatibility of their fibrinogen constituentwith the added advantage of enhanced precision in controlling thephysical properties of the polymeric network using the synthetic F127constituent.

It was shown that the conjugation reaction does not eliminate theself-assembly properties of the F127, but rather enhances it, thusendowing the obtained protein-polymer conjugates with reverse thermalgelation (RTG) properties. Thus, it was uncovered that thepoloxamer-fibrinogen conjugate surprisingly undergoes gelation at lowconcentrations (e.g., below 20 mg/ml conjugate), which are considerablylower than the concentrations necessary for reverse thermal gelation ofthe poloxamer alone. This indicates that the protein acts as a chainextender that allows the poloxamer-protein conjugate to undergo gelationat these exceptionally lower concentrations.

The ability to obtain hydrogels at low conjugate concentrations isadvantageous for applications such as tissue regeneration, because suchhydrogels are better suited for allowing cell growth and migrationwithin a hydrogel.

Using a combination of photo-polymerization cross-linking andtemperature, an exceptional control over physical properties of thegenerated hydrogels was demonstrated. The ability of the generatedhydrogels to act as a matrix for cell and tissue growth and survival hasalso been demonstrated.

Referring now to the drawings, FIGS. 1A and 1B illustrate the synthesisof an exemplary F127 poloxamer-fibrinogen conjugate.

FIG. 2 shows the gelation of the conjugate by an increase of temperature(i.e., reverse thermal gelation) at various concentrations, including atconjugate concentrations below 20 mg/ml. Such concentrations are lowerthan the concentrations that allow reverse thermal gelation of F127poloxamer alone, indicating that conjugation to fibrinogen enhanced theRTG properties of the poloxamer by acting as a chain extender.

FIGS. 3A and 3B show that the reverse thermal gelation of the conjugateis reversible, such that gelation can be repeatedly induced andreversed, even after the conjugate has been covalently cross-linked(FIG. 3B). FIG. 6 shows the reverse thermal gelation of covalentlycross-linked conjugate at various concentrations.

FIG. 4 illustrates two types of cross-linking which molecules of theconjugate can undergo to form a hydrogel; a reversibletemperature-dependent cross-linking of conjugate molecules (by reversethermal gelation), and an irreversible cross-linking induced by UVlight. FIG. 5 shows increases in shear storage modulus resulting fromboth reversible and irreversible cross-linking of conjugate molecules.

FIGS. 7A and 7B show the different behaviors of exemplary covalentlycross-linked and non-covalently cross-linked hydrogels in response tostress. FIGS. 7A and 7B also show that after collapsing in response tostress, both types of hydrogel recover completely after lowering andincreasing the temperature so as to undo and restore the reverse thermalgelation.

FIGS. 8 and 12 show that the shear storage modulus of exemplarycovalently cross-linked hydrogels depends strongly on the temperature atwhich the conjugate is covalently cross-linked. FIG. 11 shows that theeffect of cross-linking temperature on biodegradability is considerablyweaker, and that biodegradability is affected more by the type ofpolymer conjugated to the protein.

FIGS. 9-10B show that the swelling properties of covalently cross-linkedpoloxamer-fibrinogen hydrogels are temperature-dependent (in contrast tocross-linked PEG-fibrinogen hydrogels), and that the degree oftemperature dependency is affected by the cross-linking temperature.

FIGS. 13A and 13B illustrate the synthesis of an exemplaryT1307-fibrinogen conjugate, wherein each T1307 moiety in the conjugatecomprises three acrylate cross-linking moieties.

FIGS. 14A and 14B show that the shear storage modulus of covalentlycross-linked T1307-fibrinogen hydrogels depends strongly on thetemperature at which the conjugate is covalently cross-linked. FIG. 15shows that the swelling properties of covalently cross-linkedT1307-fibrinogen hydrogels are temperature-dependent, and that thedegree of temperature dependency is affected by the cross-linkingtemperature. FIG. 16 shows that that biodegradability is not clearlycorrelated with the cross-linking temperature.

The results presented in FIGS. 14A-16 indicate that the properties ofT1307-containing hydrogels are similar to those of F127poloxamer-containing hydrogels.

FIGS. 17-22 and 24A-27B show that exemplary hydrogels can serve asmatrices for cell growth and invasion, and that the rate and type ofcellular growth and invasion depends on the covalent cross-linkingtemperature of the hydrogels. FIGS. 26A-27B show the effects ofdifferent hydrogel properties on cell growth in a co-culture ofdifferent cell types.

FIGS. 23A and 23B illustrate an exemplary process for preparing ahydrogel capsule with one set of physical properties, embedded within ahydrogel with a different set of physical properties.

Thus, it has been demonstrated that polymer-fibrinogen conjugatesaccording to exemplary embodiments of the invention can be readilycross-linked so as to form hydrogel scaffolds. In addition, non-covalentand covalent cross-linking can be readily combined. The hydrogelsexhibit high flexibility, biodegradability, good biofunctionality andsupport for cell spreading and invasion, and a shear storage moduluswhich can be readily controlled by various parameters. The temperatureat which covalent cross-linking is performed was particularly useful forcontrolling the shear storage modulus, as it has relatively littleeffect on other properties, such as biodegradability.

According to one aspect of the present invention, there is provided aconjugate comprising a polypeptide having attached thereto at least twopolymeric moieties, at least one of the polymeric moieties exhibiting areverse thermal gelation. In some embodiments, each of the polymericmoieties exhibits a reverse thermal gelation.

As used herein, the phrase “reverse thermal gelation” describes aproperty whereby a substance (e.g., an aqueous solution of a compound)increases in viscosity upon an increase in temperature. The increase inviscosity may be, for example, conversion from a liquid state to asemisolid state (e.g., gel), conversion from a liquid state to a moreviscous liquid state, or conversion from a semisolid state to a morerigid semisolid state. Herein, all such conversions are encompassed bythe term “gelation”. The increase in temperature which effects gelationmay be between any two temperatures. Optionally, the gelation iseffected at a temperature within the range of 0° C. to 55° C.

Herein, a polymeric moiety is considered to exhibit a reverse thermalgelation when an aqueous solution of a polymer which corresponds to thepolymeric moiety (e.g., a polymer not attached to the abovementionedpolypeptide) exhibits a reverse thermal gelation, as described herein.

A variety of polymers exhibit a reverse thermal gelation. Each polymermay be characterized by a critical gelation temperature, whereingelation is effected at the critical gelation temperature or attemperatures above the critical gelation temperature.

Herein, “critical gelation temperature” refers to the lowest temperatureat which some gelation of a material is observed (e.g., by increase inshear storage modulus).

The polymeric moiety may be selected so as to impart to the conjugatecontaining same a reverse thermal gelation that is characterized by acritical gelation temperature within a temperature range (e.g., in arange of 0° C. to 55° C.) which allows for convenient manipulation ofthe properties of the conjugate by exposure to an ambient temperatureabove and/or below the critical gelation temperature.

The critical gelation temperature of the polymer may be selected, forexample, based on the intended use or desired properties of a conjugate.For example, the critical gelation temperature may be selected such thatthe conjugate is in a gelled state at a physiological temperature butnot at room temperature, such that gelation may be effected in vivo. Inanother example, the critical gelation temperature may be selected suchthat the conjugate is in a gelled state at room temperature but not at amoderately lower temperature, such that gelation may be effected, forexample, by removal from refrigeration.

The polymeric moiety optionally comprises a synthetic polymer.Poloxamers (e.g., F127 poloxamer) are exemplary polymers which exhibit areverse thermal gelation at temperatures suitable for embodiments of thepresent invention.

As used herein and in the art, a “poloxamer” refers to poly(ethyleneoxide) (PEO)-poly(propylene oxide) (PPO) block copolymer having aPEO-PPO-PEO structure. Suitable poloxamers are commercially available,for example, as Pluronic® polymers.

Typically, reverse thermal gelation is mediated by the formation ofnon-covalent cross-linking (e.g., via hydrophobic interactions, ionicinteractions, and/or hydrogen bonding) between molecules, wherein thedegree of non-covalent cross-linking increases in response to anincrease of temperature.

Herein, “non-covalent” cross-linking (formed as a result of a reversethermal gelation) is also referred to as “physical” cross-linking or as“non-chemical cross-linking”. The non-covalent cross-linking cantherefore be understood as a temperature-dependent cross-linking.

The polymeric moiety may comprise one or more moieties which effectnon-covalent cross-linking (e.g., hydrophobic moieties). The degree ofgelation and the conditions (e.g., temperature) under which gelation iseffected may optionally be controlled by the nature and the number ofmoieties which participate in non-covalent cross-linking.

The polymeric moiety may comprise from 1 and up to 100 and even 1000moieties which participate in non-covalent cross-linking. In manyembodiments, the higher the number of such moieties, and the larger themoieties are (e.g., the higher the molecular weights are), the lower thetemperature under which gelation is effected.

The polymeric moiety may comprise one or more types of moieties whicheffect cross-linking. These moieties may effect non-covalentcross-linking via the same intermolecular interactions (e.g.,hydrophobic interactions) or via different intermolecular interactions(e.g., hydrophobic and ionic interactions). Polymers that exhibitreverse thermal gelation (also referred to in the art as RTG polymers)include, but are not limited to, poly(N-isopropylacrylamide), whichundergoes reverse thermal gelation at temperatures above about 32-33°C., as well as copolymers thereof (e.g.,poly(N-isopropylacrylamide-co-dimethyl-γ-butyrolactone), poly(ethyleneglycol)-poly(amino urethane) (PEG-PAU) block copolymers,poly(ε-caprolactone)-poly(ethylene glycol) (PCL-PEG) block copolymers(e.g., PCL-PEG-PCL), and poly(methyl 2-propionamidoacrylate). Inaddition, polyorganophosphazenes with PEG and hydrophobic oligopeptideside groups (which provide intermolecular hydrophobic interactions) havebeen described, which are gelled at temperatures of 35-43° C. [Seong etal., Polymer 2005, 46:5075-5081].

For example, a poloxamer moiety comprises a hydrophobic PPO moiety whichmediates gelation. A polymeric moiety may optionally comprise one suchPPO moiety, or alternatively, a plurality (e.g., 2, 3, 4, etc., up to100 and even 1000 such moieties) of such moieties.

Similarly PCL-PEG copolymers comprise hydrophilic PEG and a relativelyhydrophobic poly(ε-caprolactone) (PCL) moiety, and PEG-PAU copolymerscomprise hydrophilic PEG and a hydrophobic poly(amino urethane) (PAU)moiety (e.g., a bis-1,4-(hydroxyethyl)piperazine-1,6-diisocyanatohexamethylene condensation polymer moiety).

Thus, in general, many block polymers exhibiting reverse thermalgelation may be prepared from a combination of hydrophilic andhydrophobic building blocks.

In some embodiments, each polymeric moiety comprises a poloxamer (e.g.,F127 poloxamer).

Optionally, a polymeric moiety comprises one poloxamer.

Alternatively or additionally, at least one polymeric moiety comprises aplurality of poloxamer moieties. Polymers comprising a plurality ofpoloxamer moieties are commercially available, for example, as Tetronic®polymers. T1307 (e.g., Tetronic®T1307) is an exemplary polymer whichcomprises four poloxamer moieties.

According to optional embodiments, at least one of the polymericmoieties further comprises at least one cross-linking moiety forcovalently cross-linking a plurality of molecules of the conjugate toone another. Optionally, the polymeric moiety comprises from 1 to 10,optionally from 1 to 5, and optionally from 1 to 3 cross-linkingmoieties.

It to be noted that the expression “cross-linking moiety” is used hereinto describe moieties that are attached to the polymeric moiety (e.g., asan end group or as pendant groups), or which form an integral part ofthe polymeric moiety, yet it differs from those moieties in thepolymeric moiety that effect non-covalent cross-linking, as describedhereinabove.

A “cross-linking moiety” as used herein thus describes moieties on thepolymeric moiety that effect covalent cross-linking, as defined herein,between molecules of the conjugate.

Herein, “covalent cross-linking” (also referred to herein as “chemicalcross-linking”) refers to a formation of a covalent bond (“cross-link”)between two or more molecules (e.g., two conjugate molecules describedherein). A molecule may be attached to a plurality of other molecules,each other molecule being attached by a different covalent bond. Thus, aplurality of molecules (e.g., at least 5, at least 10, at least 20, atleast 50, at least 100) may be linked together.

A conjugate as described may optionally be represented by the generalformula:

X(—Y—Zm)n

wherein X is a polypeptide as described herein, Y is a polymeric moietyas described herein, Z is a cross-linking moiety as described herein, nis an integer greater than 1 (e.g., 2, 3, 4 and up to 20), and mrepresents the number of cross-linking moieties per polymeric moiety.Thus, m is 0 in embodiments lacking the optional cross-linking moiety,and m is 1 or an integer greater than 1, in embodiments which comprisethe optional cross-linking moiety.

It is to be understood that as the above formula includes more than one—Y—Zm moiety, different —Y—Zm moieties in a conjugate may optionallyhave a different values for m.

As used herein, the phrase “cross-linking moiety” refers to a moiety(e.g., a functional group) characterized by an ability to effectcovalent cross-linking with a functional group of another molecule(e.g., another conjugate).

According to optional embodiments, the cross-linking moiety is able toeffect cross-linking with a conjugate similar to and/or identical to theconjugate described herein (e.g., a conjugate comprising a cross-linkingmoiety chemically related to and/or identical to the cross-linkingmoiety of the conjugate described herein).

Thus, the cross-linking moiety described herein provides a conjugatewith an ability to undergo covalent cross-linking, whereas a polymericmoiety which exhibits reverse thermal gelation, as described herein,provides a conjugate with an ability to undergo non-covalentcross-linking (self-assembly). Hence, in embodiments without across-linking moiety (e.g., wherein m in the general formula is 0),cross-linking of the conjugate may be effected solely by non-covalentcross-linking by the polymeric moiety, whereas in embodiments with across-linking moiety (e.g., wherein m in the general formula is 1 ormore), cross-linking of the conjugate may be effected by non-covalentcross-linking and/or by covalent cross-linking, as discussed in moredetail herein.

Exemplary cross-linking moieties that are suitable for use in thecontext of embodiments of the invention include, but are not limited to,polymerizable groups, as further detailed hereinbelow.

Thus, in some embodiments, the cross-linking moiety comprises apolymerizable group, such that cross-linking may be effected bypolymerization of the polymerizable group. In the context of embodimentsof the present invention, the polymerizable groups may act as monomers,whereby polymerization of the polymerizable groups cross-links theconjugates comprising the polymerizable groups.

Many polymerizable groups are known in the art, including groups (e.g.,unsaturated groups) which readily undergo free radical polymerization,and cyclic groups (e.g., lactones) which readily undergo polymerizationvia ring-opening. Polymerization can be effected, for example, viaphotoinitiation (in the presence of an appropriate light, e.g., 365 nm),via chemical cross-linking (in the presence of a free-radical donor)and/or heating (at the appropriate temperatures).

In some embodiments, a polymerizable group is selected such thatpolymerization thereof may be effected under relatively mild conditionswhich are non-harmful to living cells. For example, the polymerizationconditions are optionally sufficiently non-toxic and non-hazardous so asto be suitable for effecting polymerization in vivo, as describedherein.

It is to be noted that covalent cross-linking can be effected also inpresence of a cross-linking agent. Such an agent is typically abifunctional chemical moiety that is capable of reacting with thecross-linking group. Examples include, but are not limited to, PEGsterminated at both ends with a reactive group that can readily reactwith the cross-linking group.

In some embodiments, the polymerizable group is polymerizable by freeradical polymerization. Examples of such groups include, withoutlimitation, an acrylate, a methacrylate, an acrylamide, amethacrylamide, and a vinyl sulfone.

According to optional embodiments, the conjugate comprises polymericmoiety which comprise a plurality cross-linking moieties which canattach to a polypeptide. For example, acrylate, methacrylate,acrylamide, methacrylamide, and vinyl sulfone, in addition to beingpolymerizable groups, are suitable for attachment to a thiol group(e.g., in a cysteine residue) via Michael-type addition.

Thus, as exemplified in the Examples section herein, a polymeric moietymay comprise a plurality of such moieties (e.g., acrylate), one of whichattached the polymeric moiety to the polypeptide, the remaining moietiesbeing cross-linking moieties as described herein.

Thus, in exemplary embodiments, the conjugate comprises poloxamerdiacrylate (e.g., F127 poloxamer diacrylate) moieties, wherein oneacrylate group in each moiety is attached to a cysteine residue of apolypeptide (e.g., denatured fibrinogen), and one acrylate group servesas a cross-linking moiety.

In additional exemplary embodiments, the conjugate comprises a polymerictetraacrylate (e.g., T1307 tetraacrylate) moieties, wherein one acrylategroup in each moiety is attached to a cysteine residue of a polypeptide(e.g., denatured fibrinogen), and three acrylate groups serve ascross-linking moieties.

The polypeptide of the conjugate is at least 10 amino acids in length,optionally at least 20 amino acids in length, and optionally at least 50amino acids in length.

The term “polypeptide” as used herein encompasses native polypeptides(either degradation products, synthetically synthesized polypeptides orrecombinant polypeptides) and peptidomimetics (typically, syntheticallysynthesized polypeptides), as well as peptoids and semipeptoids whichare polypeptide analogs, which may have, for example, modificationsrendering the polypeptides more stable while in a body or more capableof penetrating into cells. Such modifications include, but are notlimited to, N-terminus modification, C-terminus modification, peptidebond modification, including, but not limited to, CH₂—NH, CH₂—S,CH₂—S═O, O═C—NH, CH₂—O, CH₂—CH₂, S═C—NH, CH═CH or CF═CH, backbonemodifications, and residue modification. Methods for preparingpeptidomimetic compounds are well known in the art and are specified,for example, in Quantitative Drug Design, C. A. Ramsden Gd., Chapter17.2, F. Choplin Pergamon Press (1992), which is incorporated byreference as if fully set forth herein. Further details in this respectare provided hereinunder.

Peptide bonds (—CO—NH—) within the peptide may be substituted, forexample, by N-methylated bonds (—N(CH₃)—CO—), ester bonds(—C(R)H—C—O—O—C(R)—N—), ketomethylen bonds (—CO—CH₂—), _-aza bonds(—NH—N(R)—CO—), wherein R is any alkyl, e.g., methyl, carba bonds(—CH₂—NH—), hydroxyethylene bonds (—CH(OH)—CH₂—), thioamide bonds(—CS—NH—), olefinic double bonds (—CH═CH—), retro amide bonds (—NH—CO—),peptide derivatives (—N(R)—CH₂—CO—), wherein R is the “normal” sidechain, naturally presented on the carbon atom. These modifications canoccur at any of the bonds along the polypeptide chain and even atseveral (2-3) at the same time.

As used herein throughout, the term “amino acid” or “amino acids” isunderstood to include the 20 naturally occurring amino acids; thoseamino acids often modified post-translationally in vivo, including, forexample, hydroxyproline, phosphoserine and phosphothreonine; and otherunusual amino acids including, but not limited to, 2-aminoadipic acid,hydroxylysine, isodesmosine, nor-valine, nor-leucine and ornithine.Furthermore, the term “amino acid” includes both D- and L-amino acids.

According to optional embodiments, the polypeptide comprises a proteinor a fragment thereof.

The protein may be a naturally occurring protein (e.g., a proteinexisting in eukaryotic and/or prokaryotic organisms, cells, cellularmaterial, non-cellular material, and the like) or a polypeptidehomologous (e.g., at least 90% homologous, optionally at least 95%homologous, and optionally at least 99% homologous) to a naturallyoccurring protein.

In some embodiments, the protein (or protein fragment) is denatured.

It is to be understood that the protein described herein may optionallycomprise more than one polypeptide chain.

In embodiments comprising a protein characterized by more than onepolypeptide chain, the conjugate described herein optionally comprisesone polypeptide of the protein.

Alternatively, the conjugate described herein comprises a plurality ofpolypeptides of the protein (e.g., all of the polypeptides of theprotein). Optionally, the plurality of polypeptides are linked together(e.g., by non-covalent and/or covalent bonds) so as to form a multimer(e.g., a dimer, a trimer, a tetramer, a hexamer, etc.), the multimerhaving attached thereto at least two polymeric moieties, as describedherein. Optionally, the polypeptides of the protein are separate (e.g.,separated by denaturation of the protein), such that the conjugatedescribed herein is a mixture of different conjugate species, whereineach of the conjugate species comprises a different polypeptide.

Optionally, the polypeptide (e.g., protein or protein fragment) isselected so as to exhibit a biological activity. Optionally, thebiological activity comprises support for cell growth and/or invasion.

Examples of proteins exhibiting a biological activity which isadvantageous in the context of embodiments of the present inventioninclude, without limitation, a cell signaling protein, an extracellularmatrix protein, a cell adhesion protein, a growth factor, protein A, aprotease and a protease substrate. Optionally, the protein is anextracellular matrix protein.

According to optional embodiments, the polypeptide comprises afibrinogen polypeptide (α, β and/or γ chains of fibrinogen) or afragment thereof. Optionally, the conjugate described herein comprisesthe α, β and γ chains of fibrinogen. In exemplary embodiments, thepolypeptide is a denatured fibrinogen (e.g., a mixture of denatured α, βand γ chains of fibrinogen).

Examples of extracellular matrix proteins include, but are not limitedto, fibrinogen (e.g., α-chain—GenBank Accession No. NP_(—)068657;(β-chain—GenBank Accession No. P02675; γ-chain—GenBank Accession No.P02679), collagen (e.g., GenBank Accession No. NP_(—)000079),fibronectin (e.g., GenBank Accession No. NP_(—)002017), vimentin (e.g.,GenBank Accession No. NP_(—)003371), elastin, fibrillin, fibulin,laminin (e.g., GenBank Accession No. NP_(—)000218) and gelatin.

Examples of cell signaling proteins include, but are not limited to, p38mitogen-activated protein kinase (e.g., GenBank Accession No.NP_(—)002736), nuclear factor kappaB (e.g., GenBank Accession No.NP_(—)003989), Raf kinase inhibitor protein (RKIP) (e.g., GenBankAccession No. XP_(—)497846), Raf-1 (e.g., GenBank Accession No.NP_(—)002871), MEK (e.g., GenBank Accession No. NP_(—)002746), proteinkinase C (PKC) (e.g., GenBank Accession No. NP_(—)002728),phosphoinositide-3-kinase gamma (e.g., GenBank Accession No.NP_(—)002640), receptor tyrosine kinases such as insulin receptor (e.g.,GenBank Accession No. NP_(—)000199), heterotrimeric G-proteins (e.g.,Galpha(i)—GenBank Accession No. NP_(—)002060; Galpha(s)—GenBankAccession No. NP_(—)000507; Galpha(q)—GenBank Accession No.NP_(—)002063), caveolin-3 (e.g., GenBank Accession No. NP_(—)001225),microtubule associated protein 1B, and 14-3-3 proteins (e.g., GenBankAccession No. NP_(—)003397).

Examples of cell adhesion proteins include, but are not limited to,integrin (e.g., GenBank Accession No. NP_(—)002202), intercellularadhesion molecule (ICAM) 1 (e.g., GenBank Accession No. NP_(—)000192),N-CAM (e.g., GenBank Accession No. NP_(—)000606), cadherin (e.g.,GenBank Accession No. NP_(—)004351), tenascin (e.g., GenBank AccessionNo. NP_(—)061978), gicerin (e.g., GenBank Accession No. NP_(—)006491),and nerve injury induced protein 2 (ninjurin2) (e.g., GenBank AccessionNo. NP_(—)067606).

Examples of growth factors include, but are not limited to, epidermalgrowth factor (e.g., GenBank Accession No. NP_(—)001954), transforminggrowth factor-β (e.g., GenBank Accession No. NP_(—)000651), fibroblastgrowth factor-acidic (e.g., GenBank Accession No. NP_(—)000791),fibroblast growth factor-basic (e.g., GenBank Accession No.NP_(—)001997), erythropoietin (e.g., GenBank Accession No.NP_(—)000790), thrombopoietin (e.g., GenBank Accession No.NP_(—)000451), neurite outgrowth factor, hepatocyte growth factor (e.g.,GenBank Accession No. NP_(—)000592), insulin-like growth factor-I (e.g.,GenBank Accession No. NP_(—)000609), insulin-like growth factor-II(e.g., GenBank Accession No. NP_(—)000603), interferon-γ (e.g., GenBankAccession No. NP_(—)000610), and platelet-derived growth factor (e.g.,GenBank Accession No. NP_(—)079484).

Examples of proteases include, but are not limited to, pepsin (e.g.,GenBank Accession No. NP_(—)055039), low specificity chymotrypsin, highspecificity chymotrypsin, trypsin (e.g., GenBank Accession No.NP_(—)002760), carboxypeptidases (e.g., GenBank Accession No.NP_(—)001859), aminopeptidases (e.g., GenBank Accession No.NP_(—)001141), proline-endopeptidase (e.g. GenBank Accession No.NP_(—)002717), Staphylococcus aureus V8 protease (e.g., GenBankAccession No. NP_(—)374168), proteinase K (PK) (e.g., GenBank AccessionNo. P06873), aspartic protease (e.g., GenBank Accession No.NP_(—)004842), serine proteases (e.g., GenBank Accession No.NP_(—)624302), metalloproteases (e.g., GenBank Accession No.NP_(—)787047), ADAMTS17 (e.g., GenBank Accession No. NP_(—)620688),tryptase-γ (e.g., GenBank Accession No. NP_(—)036599), matriptase-2(e.g., GenBank Accession No. NP_(—)694564).

Examples of protease substrates include the peptide or peptide sequencesbeing the target of the protease protein. For example, lysine andarginine are the target for trypsin; tyrosine, phenylalanine andtryptophan are the target for chymotrypsin.

Such naturally occurring proteins can be obtained from any knownsupplier of molecular biology reagents.

As exemplified in the Examples section below, it has been surprisinglyuncovered that a conjugate comprising a polypeptide as described hereinand at least one polymeric moiety exhibiting thermal gelation mayprovide the conjugate with an ability to undergo reverse thermalgelation.

Hence, according to optional embodiments, the conjugate is characterizedby an ability to undergo reverse thermal gelation in an aqueoussolution, as described herein.

Optionally, the reverse thermal gelation of the conjugate occurs at atemperature below 55° C., optionally below 50° C., optionally below 40°C., and optionally below 30° C. Optionally, the reverse thermal gelationoccurs at a temperature below about 37° C., such that at a physiologicaltemperature of about 37° C., the conjugate is in a gelled state.

Optionally, the reverse thermal gelation of the conjugate occurs at atemperature above 0° C., optionally above 10° C., optionally above 20°C. and optionally above 30° C.

In some embodiments, the reverse thermal gelation of the conjugateoccurs upon an increase of temperature from 0° C. to 55° C., optionallyfrom 10° C. to 55° C., optionally from 10° C. to 40° C., optionally from15° C. to 37° C., and optionally from 20° C. to 37° C. Reverse thermalgelation which occurs upon an increase of temperature from a roomtemperature (e.g., about 20° C., about 25° C.) to a physiologicaltemperature (e.g., about 37° C.) are particularly useful for someapplications (e.g., medical applications), as gelation can be induced bytransferring the conjugate from a room temperature environment to aphysiological temperature, for example, by placing the conjugate in abody.

As exemplified herein, the temperature at which gelation of a conjugatesolution occurs may be controlled by varying the concentration of theconjugate.

Furthermore, the gelation temperature may be controlled by selecting apolymer with an appropriate gelation temperature for inclusion in thepolymeric moiety, and/or by varying the concentration of polymericmoieties which exhibit reverse thermal gelation (e.g., by varying thenumber of polymeric moieties attached to a polypeptide and/or by varyingthe size of the polymeric moieties).

As further exemplified in the Examples section, aqueous solutionscomprising conjugates described herein may undergo reverse thermalgelation at relatively low concentrations, for example, less than 20weight percents conjugate, optionally less than 10 weight percents,optionally less than 5 weight percents, and optionally less than 2weight percents.

Without being bound by any particular theory, it is believed thatconjugation of a polypeptide to a polymer exhibiting reverse thermalgelation acts as chain extension of the polymer, which lowers theminimal concentration necessary for gelation.

It is to be noted that a phenomenon of a chain extender of a biologicalnature or origin (e.g., a polypeptide) has never been reportedheretofore.

The reverse thermal gelation of the conjugate as described herein can bedetermined by measuring a shear storage modulus of an aqueous solutioncontaining same. An temperature-dependent increase in the storagemodulus is indicative of a gel formation via a reverse thermal gelation.

As used herein and in the art, a “shear modulus” is defined as the ratioof shear stress to the shear strain. The shear modulus may be a complexvariable, in which case the “storage modulus” is the real component andthe “loss modulus” is the imaginary component. The storage modulus andloss modulus in viscoelastic solids measure the stored energy,representing the elastic portion, and the energy dissipated as heat,representing the viscous portion.

In some embodiments, the reverse thermal gelation described hereinincreases a shear storage modulus (also referred to herein as “storagemodulus”, or as “G′”) of the aqueous solution of the conjugate by atleast ten-folds, optionally at least 30-folds, optionally at least100-folds, and optionally at least 300-folds.

In some embodiments, the reverse thermal gelation described hereinincreases a shear storage modulus of the aqueous solution to at least 5Pa, optionally at least 15 Pa, optionally at least 20 Pa, optionally atleast 50 Pa, optionally at least 100 Pa, and optionally at least 200 Pa.

In some embodiments, the shear storage modulus of the aqueous solutioncontaining the conjugate before reverse thermal gelation (e.g., at atemperature below a temperature at which gelation occurs) is less than 2Pa, optionally less than 1 Pa, optionally less than 0.5 Pa, andoptionally less than 0.2 Pa.

According to optional embodiments, the reverse thermal gelation isreversible, i.e., a gelled state obtained by increasing a temperaturecan revert to the non-gelled state by lowering the temperature, thenon-gelled state having substantially the same properties as existedprior to the reverse thermal gelation. Reversible gelation isadvantageous in that a gelled state can be modified and/or reconstructedby causing at least a portion of the gelled state to revert to anon-gelled state (by decreasing a temperature), followed by formation ofa gelled state (by increasing a temperature) in a desired form. Inaddition, reversible gelation does not create spoilage of a product bygelation before a product is used (e.g., a product in storage), as anysuch gelation prior to use of the product may be eliminated (bycooling).

Optionally, the gelation is reversible over many cycles (e.g., at least10 cycles, at least 50 cycles) of increasing and decreasing atemperature.

Optionally, a gel formed by reverse thermal gelation of an aqueoussolution of the conjugate is a biodegradable gel, i.e., the gel degradesin contact with a tissue and/or a cell (e.g., by proteolysis and/orhydrolysis). Biodegradable materials are useful in various medicalapplications, for example as temporary implants. In addition,biodegradable materials are highly suitable as matrices for supportingcell growth and/or migration, as cell growth and/or migration isassociated with degradation of a surrounding matrix.

As exemplified in the Examples section below, a gel formed by reversethermal gelation of a solution of a conjugate described herein may serveas a suitable matrix for cell growth, spreading, expansion and/orinvasion.

Hence, the conjugate described herein is optionally identified for usein generating a scaffold, as defined herein. The scaffold may begenerated by reverse thermal gelation of the conjugate (e.g., bynon-covalent cross-linking of the conjugate) and/or by covalentcross-linking of the conjugate.

The conjugate described herein can therefore be referred to also as aprecursor molecule for generating a scaffold. Thus, the scaffold isformed by cross-linking (covalently and/or non-covalently) a pluralityof precursor molecules to one another.

As used herein, the term “scaffold” describes a two-dimensional or athree-dimensional supporting framework. The scaffold according toembodiments of the present invention is composed of precursor units(comprising the conjugates as described herein) which are cross-linkedtherebetween. In some embodiments, a scaffold can be used as a supportfor cell growth, attachment and/or spreading and thus facilitates tissuegeneration and/or tissue repair. In some embodiments, a scaffoldmaintains a desired shape of a tissue and/or cell colony supportedthereby.

In exemplary embodiments, the scaffold is a hydrogel, i.e., the gelformed from the conjugate comprises water absorbed therein, for example,water from an aqueous solution of the conjugate which underwentgelation.

As used herein and is well-known in the art, the term “hydrogel” refersto a material that comprises solid networks formed of water-solublenatural or synthetic polymer chains, typically containing more than 99%water.

Optionally the hydrogel is characterized by a shear storage modulus ofat least 15 Pa (optionally at least 50 Pa, optionally at least 100 Pa,and optionally at least 200 Pa) at 37° C.

Optionally the generation of the scaffold is reversible. Reversiblescaffold generation is optionally obtained in embodiments whereinscaffold generation is by reverse thermal gelation, as discussedhereinabove.

Optionally, the scaffold is generated by means other than reversethermal gelation, for example, by covalent cross-linking. The obtainedscaffold (e.g., a hydrogel) is optionally capable of further undergoinga reverse thermal gelation. Further optionally, the scaffold isgenerated by a reverse thermal gelation and is thereafter furthersubjected to covalent cross-linking, as described herein.

As discussed herein, conjugates described herein may be cross-linked bynon-covalent (physical) cross-linking and/or by covalent (chemical)cross-linking.

Hence, according to another aspect of embodiments of the invention,there is provided a composition-of-matter (e.g., a scaffold or ahydrogel) comprising a cross-linked form of a conjugate describedherein. The composition-of-matter thus comprises a plurality ofmolecules of the conjugate cross-linked to one another.

It is to be understood that although the composition-of-matter isdescribed herein for the sake of simplicity as comprising a conjugate,compositions-of-matter comprising a plurality of conjugate species(e.g., a mixture of different conjugates) are encompassed by the term“composition-of-matter”.

In some embodiments, the conjugate molecules are cross-linkednon-covalently.

Optionally the molecules are cross-linked only non-covalently (i.e., nosubstantial covalent cross-linking is present).

Compositions-of-matter described herein may optionally be generated bynon-covalent and/or covalent cross-linking of the conjugate molecules ina solution, preferably an aqueous solution. Optionally, the solutionremains absorbed to the cross-linked conjugate, for example, in the formof a gel (e.g., a hydrogel).

The solution may be selected suitable for effecting the abovementionedcovalent and/or non-covalent cross-linking.

In some embodiments, the solution is an aqueous solution.

Compositions-of-matter comprising only non-covalent cross-linking mayoptionally be generated by reverse thermal gelation of the conjugatemolecules in an aqueous solution (e.g., as described herein).Optionally, the non-covalently cross-linked form is reversible, asdescribed herein.

In some embodiments, the conjugate molecules are cross-linkedcovalently. In such embodiments, the conjugate comprises a cross-linkingmoiety (as described herein). The composition-of-matter is optionallygenerated by subjecting a plurality of conjugate molecules to conditionsfor effecting covalent cross-linking of the cross-linking moieties ofthe conjugate molecules.

Optionally the covalently cross-linked composition-of-matter ischaracterized by a shear storage modulus of at least 20 Pa at 37° C.,and optionally at least 50 Pa, optionally at least 100 Pa, optionally atleast 200 Pa, and optionally at least 300 Pa.

In some embodiments a composition-of-matter comprises non-covalentcross-linking, in addition to the covalent cross-linking.

For example, a composition-of-matter comprising covalent cross-linkingmay be capable of undergoing reverse thermal gelation (e.g., areversible reverse thermal gelation).

Such a reverse thermal gelation of a covalently cross-linkedcomposition-of-matter may optionally increase a shear storage modulus ofthe composition-of-matter by at least 20%, optionally at least 50%,optionally at least 200%, optionally at least 400%, and optionally atleast 900%.

The shear storage modulus prior to reverse thermal gelation isoptionally in a range of from 0.5 Pa to 200 Pa, optionally in a range offrom 0.5 Pa to 100 Pa, and optionally in a range of from 10 Pa to 100Pa.

The shear storage modulus following reverse thermal gelation isoptionally at least 15 Pa, and optionally in a range of from 20 Pa to5000 Pa, optionally from 20 Pa to 1000 Pa, optionally from 20 Pa to 500Pa, and optionally from 50 Pa to 500 Pa.

Optionally, the reverse thermal gelation of a covalently cross-linkedcomposition-of-matter is at a temperature described herein for gelationof a conjugate.

As exemplified in the Examples section below, a composition-of-mattermay be characterized by a shear storage modulus of one portion of thecomposition-of-matter that is different from a shear storage modulus ofat least one other portion of the composition-of-matter. Each portionmay independently be characterized by non-covalent cross-linking,covalent cross-linking or a combination of non-covalent and covalentcross-linking (e.g., as described hereinabove).

Such a composition-of-matter may be prepared, for example, using twosolutions of a conjugate (e.g., solutions of different conjugates and/orsolutions with different concentrations of conjugate). Optionally, onesolution is cross-linked to obtain a first composition-of-matter (e.g.,as described herein), whereupon the first composition-of-matter is addedto the second solution. Upon cross-linking of the second solution (e.g.,under conditions which do not significantly affect the firstcomposition-of-matter), a composition-of-matter having portions withdifferent properties may be obtained.

Regardless of the type (non-covalent and/or covalent) of cross-linking,compositions-of-matter described herein are optionally biodegradable. Insome embodiments, the incorporation of a polypeptide in a network ofcross-linked conjugates within the composition-of-matter causes thecomposition-of-matter to biodegrade upon biodegradation of thepolypeptide.

According to optional embodiments, the composition-of-matter furthercomprises cells (preferably live cells) therein. The cells may compriseone cell type or a two or more cell types.

Compositions-of-matter described herein may be useful for inducingformation of a tissue, for example, by serving as a matrix forsupporting cellular growth and/or invasion, and/or by providing cells(e.g., embedded in the composition-of-matter) which induce tissueformation. Such properties may be useful for repairing tissue damage.

Hence, in some embodiments, the composition-of-matter is identified foruse in inducing formation of a tissue, as discussed in further detailhereinbelow.

In some embodiments, the composition-of-matter is identified for use inrepairing tissue damage, as discussed in further detail hereinbelow.

The compositions-of-matter described herein may be prepared by variousprocesses, depending on the type of composition-of-matter, andparticularly, on the type of cross-linking (i.e., non-covalent and/orcovalent) in the composition-of-matter.

Thus, according to another aspect of embodiments of the invention, thereis provided a process of producing a composition-of-matter whichcomprises non-covalent cross-linking (e.g., as described herein). Theprocess comprises heating a solution (e.g., an aqueous solution) whichcomprises a plurality of molecules of a conjugate as described herein,from a first temperature to a second temperature. The second temperatureis such that a reverse thermal gelation of the conjugate in solution iseffected, thereby producing a composition-of-matter with non-covalentcross-linking.

The second temperature is a temperature at or above the criticaltemperature of the precursor conjugate, as detailed hereinabove.

Optionally, the composition-of-matter is produced in vivo, for example,by heating to a physiological temperature (e.g., about 37° C.). Suchheating may be effected simply by contacting a solution of the conjugatewith a body.

In some embodiments, the conjugate is a conjugate comprising at leastone cross-linking moiety described herein, and the process furthercomprises subjecting the conjugate solution to conditions that effectcross-linking of the cross-linking moieties (e.g., prior to theaforementioned heating, subsequent to the heating or concomitant withthe heating). Cross-linking of the cross-linking moieties may optionallybe performed so as to obtain a composition-of-matter comprising bothnon-covalent and covalent cross-linking.

According to another aspect of embodiments of the invention, there isprovided a process of producing a composition-of-matter which comprisescovalent cross-linking (e.g., as described herein). The processcomprises subjecting a solution comprising a plurality of molecules of aconjugate described herein, wherein the conjugate comprises at least onecross-linking moiety (as described herein), to conditions that effectcovalent cross-linking of the cross-linking moieties, thereby producinga composition-of-matter with covalent cross-linking.

Optionally, the covalent cross-linking is effected in vivo.

Alternatively, the covalent cross-linking is effected ex vivo.

Optionally, the process further comprises forming non-covalentcross-links, for example, by exposure to a temperature at which reversethermal gelation occurs.

In some embodiments, covalent cross-linking is effected ex vivo, tothereby produce a covalently cross-linked scaffold, and the processfurther comprises subjecting the covalently cross-linked scaffold to aphysiological temperature in vivo (e.g., by contacting the scaffold witha body), such that reverse thermal gelation of the scaffold is effectedin vivo, thereby producing a composition-of-matter in vivo whichcomprises non-covalent and covalent cross-linking.

In some embodiments, the solution of the conjugate further comprisescells. Consequently, the process produces a composition-of-mattercomprising cells embedded therein (as described herein).

The conditions which effect cross-linking of cross-linking moieties willdepend on the chemical properties of the cross-linking moieties.

Various conditions for effecting cross-linking are known in the art. Forexample, cross-linking may be effected by irradiation (e.g., by UVlight, by visible light, by ionizing radiation), by an initiator (e.g.,free radical donors) and/or heat.

Preferably, the conditions for effecting covalent cross-linking arebiocompatible, namely, use agents or conditions which are not consideredas hazardous in in vivo applications.

According to an optional embodiment of the present invention, thecross-linking is by illumination with UV (e.g., at a wavelength of about365 nm).

As used herein the term “about” refers to ±10%.

When cross-linking in vivo, it is preferable to avoid irradiation dosesthat are harmful. The maximal dose which is non-harmful will depend, forexample, on the type (e.g., wavelength) of irradiation, and on the partof the body exposed to the irradiation. One skilled in the art willreadily be capable of determining whether a dose is harmful ornon-harmful.

In some embodiment, the conditions comprise a presence of an initiatorwhich is added to facilitate cross-linking.

Optionally, the initiator is capable of effecting cross-linking withoutirradiation.

Alternatively, the initiator is a photoinitiator which effectscross-linking in the presence of irradiation (e.g., UV light, visiblelight). Addition of a photoinitiator will typically enable one to uselower doses of UV light for cross-linking.

As used herein, the term “photoinitiator” describes a compound whichinitiates a chemical reaction (e.g., cross-linking reaction, chainpolymerization) when exposed to UV or visible illumination. Manysuitable photoinitiators will be known to one skilled in the art.Exemplary photoinitiators include, without limitation,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO),2,2-dimethoxy-2-phenylacetophenone (DMPA), camphorquinone (CQ),1-phenyl-1,2-propanedione (PPD), the organometallic complexCp′Pt(CH(3))(3) (Cp′=eta(5)-C(5)H(4)CH(3)),2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (e.g.,Irgacure™ 2959), dimethylaminoethyl methacrylate (DMAEMA),2,2-dimethoxy-2-phenylacetophenone, benzophenone (BP), and flavins.

As exemplified in the Examples section below, physical properties (e.g.,shear storage modulus) of compositions-of-matter depend on certainparameters which may be readily controlled. Thus, acomposition-of-matter having a desired physical property may be preparedby selecting a suitable value of one or more of such parameters.

Hence, according to another aspect of embodiments of the invention,there is provided a method of controlling a physical property (e.g., ashear storage modulus) of a composition-of-matter such as describedherein. The method comprises controlling a parameter which characterizesthe composition-of-matter. Such a parameter can be, for example, aconcentration of a conjugate described herein in the solution (aqueoussolution), an ambient temperature, a cross-linking temperature. Inaddition, the parameter can be the presence or absence of covalentcross-linking, a concentration of initiator (e.g., a presence or absenceof initiator) during covalent cross-linking, and/or a dose ofirradiation used for covalent cross-linking.

The concentration of a conjugate in a composition-of-matter may bereadily controlled by preparing a solution of the conjugate at aselected concentration, and cross-linking the conjugate by covalentand/or non-covalent cross-linking, as described herein, such that thesolution of the conjugate is converted into a composition-of-matterdescribed herein, having the selected concentration of conjugate.

In some embodiments, the concentration of conjugate is positivelycorrelated with the shear storage modulus, as exemplified in theExamples herein.

In some embodiments, the concentration of conjugate is negativelycorrelated with a temperature at which reverse thermal gelation iseffected (e.g., a critical gelation temperature), as exemplified in theExamples herein.

In some embodiments, the ambient temperature controls a physicalproperty of a composition-of-matter by affecting reverse thermalgelation of a composition-of-matter, as described herein.

The ambient temperature may be selected, for example, such that gelationis not effected (e.g., at a relatively low temperature) and the shearstorage modulus is relatively low, such that gelation is effected (e.g.,at a relatively high temperature) and the shear storage modulus isrelatively high. In addition, an ambient temperature may be selected(e.g., at an intermediate temperature) such that gelation is partiallyeffected to any desired degree, such that the shear storage can be atany intermediate level which is desired.

Typically, the composition-of-matter will be characterized by arelatively narrow temperature range (e.g., a 5° C. range, a 10° C.range, a 15° C. range) in which a physical property (e.g., a shearstorage modulus) exhibits a particularly strong temperature dependence.Optionally, an ambient temperature is selected from within thistemperature range, such that the physical property may be convenientlycontrolled by relatively small changes in ambient temperature.

The cross-linking temperature (i.e., a temperature at which conjugatesin the composition-of-matter are covalently cross-linked) may be used tocontrol a physical property of a composition-of-matter which comprisescovalent cross-linking (e.g., as described herein).

In some embodiments, the cross-linking temperature is negativelycorrelated with a shear storage modulus of the composition-of-matter, asexemplified in the Examples herein.

In some embodiments, a correlation between a physical property (e.g.,shear storage modulus) and cross-linking temperature is particularlystrong when the cross-linking temperature is in a temperature range inwhich a physical property exhibits a particularly strongtemperature-dependence, as described hereinabove. Optionally across-linking temperature is selected from within this temperaturerange, such that the physical property may be conveniently controlled byrelatively small changes in cross-linking temperature.

In some embodiments, the presence of covalent cross-linking isassociated with a higher shear storage modulus, as exemplified herein.

In some embodiments, a degree of covalent cross-linking by modulatingthe conditions for effecting covalent cross-linking.

Thus, for example, low degree of covalent cross-linking may be obtainedby effecting covalent cross-linking without an initiator or with asmaller amount of initiator, and/or without irradiation or with a smalldose of irradiation (e.g., using a short irradiation time and/or a lowintensity of irradiation).

In some embodiments, the parameter (e.g., ambient temperature,cross-linking temperature) is relatively independent of some physicalproperties (e.g., biodegradation rate). This advantageously allows forcontrolling two or more physical properties of interest (e.g.,degradation rate and shear storage modulus) without creating a need forexperimentation to determine how such physical properties areinterdependent. For example, a shear storage modulus may optionally becontrolled by selecting a suitable cross-linking temperature, while adegradation rate may be controlled by selecting an appropriate polymerfor the polymeric moieties described herein.

Thus, in some embodiments, changing a parameter described herein (e.g.,ambient temperature, cross-linking temperature) will change abiodegradation rate by a factor of less than 4, optionally by a factorof less than 3, optionally by a factor of less than 2, and optionally bya factor of less than 1.5.

The biodegradation rate is optionally quantified by measuring ahalf-life of the composition-of-matter in a trypsin solution (e.g.,using procedures described herein).

Conjugates according to embodiments of the invention may be produced ina relatively simple and inexpensive manner.

Thus, according to another aspect of embodiments of the invention, thereis provided a process of producing a conjugate as described herein, theprocess comprising covalently attaching a polymer to a polypeptide, thepolymer and polypeptide being such that at least two polymer moleculesattach to a molecule of the polypeptide, wherein at least one of the twopolymer molecules exhibits a reverse thermal gelation.

The polymer may optionally comprise at least one cross-linking moiety(e.g., as described herein), so as to produce a conjugate comprising atleast one cross-linking moiety, as described herein.

Optionally, the polymer comprises at least one first moiety (optionallya single first moiety) which is capable of reacting so as to attach thepolymer to the polypeptide, and optionally at least one second moietywhich is a cross-linking moiety described herein.

In some embodiments, the first moiety and the second moiety aredifferent, such that the first moiety may be reacted so as to attach thepolymer to the polypeptide, without causing the second moiety(cross-linking moiety) to react prematurely (e.g., before cross-linkingof conjugate molecules is desired).

In some embodiments, the first moiety and second moiety are the same,the moiety being suitable for attaching the polymer to the polypeptideand for cross-linking the conjugate.

Optionally, such a cross-linking moiety is selected as being capable ofundergoing two different reactions, each under different conditions,such that the moiety may be reacted under one set of conditions so as toattach the polymer to the polypeptide, and then reacted under differentconditions so as to cross-link conjugate molecules. For example, asdescribed herein, some unsaturated moieties (e.g., acrylates) mayundergo Michael-type addition by a thiol (e.g., under basic conditions)so as to attach the polymer to a polypeptide, and also undergopolymerization (e.g., under conditions for initiating free radicalpolymerization) so as to cross-link conjugates.

In some embodiments wherein the first and second moieties describedherein are the same (or otherwise capable of undergoing similarreactions under the same conditions), the polypeptide is reacted with amolar excess (e.g., at least 20:1, at least 50:1, at least 100:1, atleast 200:1) of the polymer, so as to prevent each polymer molecule fromattaching to more than one site on the polypeptide.

Apart from being inexpensive to produce, the compositions-of-matter ofembodiments of the present invention are highly reproducible, flexible(can be stressed or stretched easily), exhibit controllable structuralproperties, and are amenable to controllable biodegradation;characteristics which make it highly suitable for in vivo or ex vivoregeneration of tissues such as bone, cartilage, heart muscle, skintissue, blood vessels, and other tissues (soft and hard) in the body.For example, such a scaffold hydrogel can be easily placed into gapswithin a tissue or an organ, following which it can fill the void andinitiate the process of regeneration as the scaffold degrades away.

Hence, according to another aspect of embodiments of the invention,there is provided a use of a conjugate described herein or of acomposition-of-matter described herein in the manufacture of amedicament for repairing tissue damage.

The medicament is optionally for inducing formation of a tissue (in vivoand/or ex vivo).

Optionally, the medicament is for treating a disorder characterized bytissue damage or loss (e.g., as described herein). Herein, the phrase“tissue” refers to part of an organism consisting of an aggregate ofcells having a similar structure and function. Examples include, but arenot limited to, brain tissue, retina, skin tissue, hepatic tissue,pancreatic tissue, bone, cartilage, connective tissue, blood tissue,muscle tissue, cardiac tissue brain tissue, vascular tissue, renaltissue, pulmonary tissue, gonadal tissue, hematopoietic tissue and fattissue. Preferably, the phrase “tissue” as used herein also encompassesthe phrase “organ” which refers to a fully differentiated structural andfunctional unit in an animal that is specialized for some particularfunction. Non-limiting examples of organs include head, brain, eye, leg,hand, heart, liver kidney, lung, pancreas, ovary, testis, and stomach.

According to another aspect of embodiments of the invention, there isprovided a use of a conjugate described herein or of acomposition-of-matter described herein in the manufacture of amedicament for treating a subject having a disorder characterized bytissue damage or loss.

As used herein the phrase “disorder characterized by tissue damage orloss” refers to any disorder, disease or condition exhibiting a tissuedamage (e.g., non-functioning tissue, cancerous or pre-cancerous tissue,broken tissue, fractured tissue, fibrotic tissue, or ischemic tissue) ora tissue loss (e.g., following a trauma, an infectious disease, agenetic disease, and the like) which require tissue regeneration.Examples for disorders or conditions requiring tissue regenerationinclude, but are not limited to, liver cirrhosis such as in hepatitis Cpatients (liver tissue), type-1 diabetes (pancreatic tissue), cysticfibrosis (lung, liver, pancreatic tissue), bone cancer (bone tissue),burn and wound repair (skin tissue), age related macular degeneration(retinal tissue), myocardial infarction, myocardial repair, CNS lesions(myelin), articular cartilage defects (chondrocytes), bladderdegeneration, intestinal degeneration, and the like. In addition,cosmetic tissue damage or loss is encompassed by the term “disorder”.

As used herein, the term “cosmetic” refers to apparent (e.g., visible)tissue, including, but not limited to, skin tissue. Cosmetic tissuedamage or loss is typically detrimental aesthetically, and may bedetrimental for additional reasons (e.g. psychological factors).

Herein, the phrase “treating” refers to inhibiting or arresting thedevelopment of a disease, disorder or condition and/or causing thereduction, remission, or regression of a disease, disorder or conditionin an individual suffering from, or diagnosed with, the disease,disorder or condition. Those of skill in the art will be aware ofvarious methodologies and assays which can be used to assess thedevelopment of a disease, disorder or condition, and similarly, variousmethodologies and assays which can be used to assess the reduction,remission or regression of a disease, disorder or condition.

In some embodiments, a medicament comprising a conjugate as describedherein is identified for being cross-linking the conjugate (in vivoand/or ex vivo), as described herein.

In some embodiments, a medicament comprising a composition-of-matterdescribed herein is identified for being implanted in a subject.

As used herein, the term “subject” refers to a vertebrate, preferably amammal, more preferably a human being (male or female) at any age.

Implantation is optionally effected using a surgical tool such as ascalpel, spoon, spatula, or other surgical devices. Optionally,implantation is effected via injection (e.g. via syringe, catheter, andthe like)

Herein, the terms “implant” and “implantation” encompass placing asubstance (e.g., a conjugate or composition-of-matter described herein)in a body or on a body surface (e.g., on a skin surface). According toanother aspect of embodiments of the invention, there is provided amethod of inducing formation of a tissue in vivo, the method comprisingimplanting a composition-of-matter described herein in a subject (e.g.,as described herein), to thereby induce the formation of the tissue.

In some embodiments, the composition-of-matter is acomposition-of-matter which comprises covalently cross-linked conjugateas described herein, and is non-covalently cross-linked in vivofollowing implantation (e.g., to provide the composition-of-matter witha desired rigidity). Optionally, the non-covalent cross-linking iseffected by exposure to a physiological temperature (e.g., as describedherein), the exposure to the physiological temperature being a directresult of implantation.

According to another aspect of embodiments of the invention, there isprovided a method of inducing formation of a tissue in vivo, the methodcomprising implanting a plurality of molecules of a conjugate describedherein in a subject, to thereby induce the formation of the tissue.

In some embodiments, the conjugate is non-covalently cross-linked invivo following implantation (e.g., to form a scaffold). Optionally, thenon-covalent cross-linking is effected by exposure to a physiologicaltemperature (e.g., as described herein), the exposure to thephysiological temperature being a direct result of implantation.

In some embodiments, the conjugate is covalently cross-linked in vivofollowing implantation (e.g., to form a scaffold). Cross-linking can beperformed as described herein, using non-toxic, non-hazardous agentsand/or conditions (e.g., application of UV irradiation).

According to another aspect of embodiments of the invention, there isprovided a method of inducing formation of a tissue ex vivo, the methodcomprising subjecting a composition-of-matter having cells therein (asdescribed herein) to conditions conductive to growth of the cells, tothereby induce tissue formation.

As used herein, the phrase “ex vivo” refers to living cells which arederived from an organism and are growing (or cultured) outside of theliving organism, for example, outside the body of a vertebrate, amammal, or human being. For example, cells which are derived from ahuman being such as human muscle cells or human aortic endothelial cellsand cultured outside of the body are referred to as cells which arecultured ex vivo.

The cells in a composition-of-matter described herein are optionallyselected so as to be capable of forming a tissue. Such cells can be, forexample, stem cells such as embryonic stem cells, bone marrow stemcells, cord blood cells, mesenchymal stem cells, adult tissue stemcells, or differentiated cells such as neural cells, retinal cells,epidermal cells, hepatocytes, pancreatic cells, osseous cells,cartilaginous cells, elastic cells, fibrous cells, myocytes, myocardialcells, endothelial cells, smooth muscle cells, and hematopoietic cells.

The composition-of-matter comprising cells may comprise cells embeddedwithin and/or on the surface of the composition-of-matter. Cells mayoptionally be embedded within the composition-of-matter by cross-linkinga conjugate described herein in the presence of cells (e.g., asdescribed herein). Incorporation of cells onto a surface of thecomposition-of-matter may optionally be effected by contacting aprepared composition-of-matter with the cells.

The concentration of cells in and/or on the composition-of-matterdepends on the cell type and the scaffold properties. Those of skill inthe art are capable of determining the concentration of cells used ineach case.

The composition-of-matter is optionally contacted with tissue culturemedium and growth factors.

Alternatively or additionally, the composition-of-matter comprisestissue culture medium and growth factors, for example, in an aqueousphase of a hydrogel.

Optionally, the cells are routinely examined (e.g., using an invertedmicroscope) for evaluation of cell growth, spreading and tissueformation, in order to facilitate control over the tissue formation,and/or to determine when a process of tissue formation has beencompleted.

Following ex vivo tissue formation, the obtained tissue and/orcomposition-of-matter comprising the formed tissue is optionallyimplanted in the subject (e.g., to induce further tissue formation, torepair tissue damage, and/or to treat a disorder as described herein).Those of skills in the art are capable of determining when and how toimplant the tissue and/or composition-of matter to thereby induce tissueformation and/or repair, and/or to treat a disease described herein.

It will be appreciated that the cells to be implanted in a subject(e.g., for inducing in vivo tissue formation and/or following ex vivoformation of a tissue), as described herein, may optionally be derivedfrom the treated subject (autologous source), and optionally fromallogeneic sources such as embryonic stem cells which are not expectedto induce an immunogenic reaction.

According to another aspect of embodiments of the invention, there isprovided a method of treating a subject having a disorder characterizedby tissue damage or loss (e.g., as described herein), the methodcomprising implanting a composition-of-matter described herein in asubject, as described herein, to thereby induce formation of the tissue,thereby treating the disorder characterized by tissue damage or loss.

According to another aspect of embodiments of the invention, there isprovided a method of treating a subject having a disorder characterizedby tissue damage or loss (e.g., as described herein), the methodcomprising implanting a plurality of molecules of a conjugate describedherein in a subject, as described herein, to thereby induce formation ofthe tissue, thereby treating the disorder characterized by tissue damageor loss.

In some embodiments of the methods described herein which are effectedby implanting a conjugate, the conjugate optionally comprises at leastone cross-linking moiety (e.g., as described herein). In suchembodiments, the method optionally further comprising covalentlycross-linking the plurality of molecules of the conjugate, for example,by subjecting the plurality of molecules to conditions (e.g., asdescribed herein) that effect covalent cross-linking of thecross-linking moieties of the molecules.

A conjugate described herein may be provided as a composition, forexample a composition for effecting a method or use described herein.The composition may be for effecting a pharmaceutical (e.g., medicinal)treatment and/or a cosmetic treatment (e.g., as described herein).

Hence, according to another aspect of embodiments of the invention,there is provided a pharmaceutical, cosmetic or cosmeceuticalcomposition comprising a plurality of molecules of a conjugate describedherein, the composition being identified for use in inducing formationof a tissue upon being contacted with a tissue and further uponsubjecting the composition to a physiological temperature.

Herein, the phrase “cosmeceutical composition” refers to a compositioncharacterized by both pharmaceutical and cosmetic uses.

Optionally, the conjugate comprises at least one cross-linking moiety(as described herein), and the composition is identified for use ininducing formation of a tissue upon further subjecting the plurality ofmolecules of the conjugate to conditions (e.g., as described herein)that effect covalent cross-linking of the cross-linking moieties of themolecules.

Optionally, the composition further comprises an initiator (e.g., asdescribed herein) for inducing the covalent cross-linking of thecross-linking moieties.

Optionally, the composition described herein is packaged in a packagingmaterial and identified in print, in or on the packaging material, foruse in inducing formation of tissue and/or for treating a disorder, asdescribed herein.

The composition may further comprise a pharmaceutically acceptablecarrier, and be formulated for facilitating its administration (e.g.,implantation).

Herein, the term “pharmaceutically acceptable carrier” refers to acarrier or a diluent that does not cause significant irritation to anorganism and does not abrogate the biological activity and properties ofthe administered compound. Examples, without limitations, of carriersare: propylene glycol, saline, emulsions and mixtures of organicsolvents with water, as well as solid (e.g., powdered) and gaseouscarriers.

Optionally, the carrier is an aqueous carrier, for example, an aqueoussolution (e.g., saline).

The conjugate may also be provided as part of a kit.

Thus, according to another aspect of embodiments of the invention, thereis provided a kit for inducing formation of a tissue, the kit comprisinga conjugate described herein, an aqueous solvent, and instructions forcross-linking an aqueous solution of the conjugate in order to form ascaffold for inducing formation of tissue.

Optionally, the conjugate and solvent are stored separately within thekit (e.g., in separate packaging units), such that the conjugate isstored in a dry state until being contacted with the solvent forformation of a solution of the conjugate (e.g., a solution describedherein). Such storage of the conjugate prior to use may increase aneffective life span of the conjugate (and kit).

Optionally, the conjugate comprises at least one cross-linking moiety(e.g., as described herein), and the kit further comprises an initiator(e.g. as described herein) for inducing covalent cross-linking of thecross-linking moiety.

Optionally, the kit further comprises cells for embedding in thescaffold (e.g., as described herein).

The cells may form a part of the solvent or may be packaged separately.

In some embodiments, the kit comprises instructions as a package insert.

Instructions for cross-linking the conjugate in the solvent can be, forexample, mixing the conjugate and solvent and subjecting the obtainedsolution to a certain temperature (e.g., for effecting reverse thermalgelation).

For example, if gelation of the conjugate is effected at ambienttemperature, instructions may be to store the kit under refrigeration(e.g., below 10° C. or at 4° C.), mix the components at room temperatureand wait until gel formation is observed.

If gelation is effected at higher temperatures, instructions may be tomix the components and then heat the solution for an indicated timeperiod.

If covalent cross-linking is to be effected by irradiation, instructionsmay be to mix the components (optionally including a photoinitiator asdescribed herein), irradiate the solution, and optionally heating thesolution to effected thermal gelation as described hereinabove. Theirradiation can be prior to, concomitant with or after irradiation.

If covalent cross-linking is to be effected by free radicalpolymerization, instructions may be to mix the components (including apolymerization initiator as described herein), and optionally heatingthe solution to effect thermal gelation as described hereinabove and/orto effect polymerization (if heating is desired). The heating to effectthermal gelation and to effect polymerization can be to the sametemperature or to different temperatures.

In some embodiments, the conjugate and the solution are packaged withinthe kit at a ratio suitable for obtaining a composition-of-matter withthe desired properties. Such a ratio can be pre-determined as detailedhereinabove.

Optionally, the instructions further include guidance for selecting asuitable ratio for obtaining a suitable property of thecomposition-of-matter, in accordance with the description providedhereinabove.

The instructions may further include guidance with regard to selectingthe cross-linking conditions (e.g., with or without irradiation; with orwithout heating; with or without adding a polymerization initiator) forobtaining a composition-of-matter with desired properties.

It is expected that during the life of a patent maturing from thisapplication many relevant polymers exhibiting reverse thermal gelationwill be developed and the scope of the phrase “polymeric moietiesexhibiting a reverse thermal gelation” is intended to include all suchnew technologies a priori.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in anon-limiting fashion.

Materials and Methods

Materials:

Acetone was obtained from Bio-Lab (Israel);

acryloyl-chloride was obtained from Merck;

calcein AM was obtained from Sigma-Aldrich;

collagen type-I was obtained from BD Biosciences;

collagenase 1A was obtained from Sigma-Aldrich;

dichloromethane was obtained from Aldrich;

diethyl ether was obtained from Frutarom (Israel);

Dulbecco's modified Eagle medium was obtained from Gibco;

ethidium homodimer-1 was obtained from Sigma-Aldrich;

fetal bovine serum was obtained from Biological Industries (Israel);

formalin was obtained from Sigma-Aldrich;

Hoechst 33342 was obtained from Sigma Aldrich;

Irgacure® 2959 initiator was obtained from Ciba;

mercaptoethanol was obtained from Gibco;

N-hydroxysuccinimide-fluorescein was obtained from Thermo Scientific;

non-essential amino acids wee obtained from Biological industries(Israel);

penicillin-streptomycin was obtained from Biological Industries(Israel);

petroleum ether 40-60 was obtained from Bio-Lab (Israel);

Pluronic® F127 (12.6 kDa) was obtained from Sigma;

poly(ethylene glycol) (12 kDa) was obtained from Fluka;

sodium azide was obtained from Riedel-deHaen;

Tetronic® tetraol T1307 was obtained from BASF;

toluene was obtained from Bio-Lab (Israel);

triethylamine was obtained from Fluka;

tris(2-carboxyethyl)phosphine hydrochloride was obtained from Sigma;

trypsin was obtained from MP Biomedicals.

F127 Poloxamer-Diacrylate, Tetronic® T1307-Tetraacrylate andPEG-Diacrylate Synthesis:

F127 poloxamer-diacrylate (F127-DA), Tetronic® T1307-tetraacrylate(T1307-TA) and poly(ethylene glycol)-diacrylate (PEG-DA) were preparedfrom Pluronic® F127 (12.6 kDa), Tetronic® tetraol T1307 (18 kDa) andpoly(ethylene glycol) (PEG) diol (12 kDa), respectively, according tothe procedures described in Halstenberg et al. [Biomacromolecules 2002,3:710-723]. As depicted in FIG. 1A, acrylation of the polymers wascarried out under argon by reacting the hydroxyl-terminated polymers ina solution of dichloromethane and toluene with acryloyl chloride (Merck,Darmstadt, Germany) and triethylamine at a molar ratio of 1.5:1 relativeto the hydroxyl groups. The final product was precipitated in ice-colddiethyl ether (for PEG-DA) or petroleum ether 40-60 (for F127-DA andT1307-TA). The solid polymer was dried under vacuum for 48 hours.

Using proton NMR, the average number of acryl groups per F127-DAmolecule was determined to be 2.15, the average number of acryl groupsper T1307-TA molecule was determined to be 4.38, and the average numberof acryl groups per PEG-DA was determined to be 1.74.

Rheological Characterization:

Rheological measurements were carried out using an AR-G2 rheometer (TAInstruments) equipped with a Peltier plate temperature-controlled base.A 40 mm quartz plate geometry was used in all experiments. Eachmeasurement was carried out with 0.4 ml of the polymer solutioncontaining 0.1% (weight/volume) Irgacure® 2959 initiator. UV light (365nm) was applied by a circular multi-diode array (Moritex, Japan). Thetesting conditions for all measurements were 2% strain at an oscillationfrequency of 1 Hz.

Water Uptake Measurements:

Hydrogel constructs were made from a volume of 100 μl polymer-fibrinogenconjugate solution with 0.1% (weight/volume) Irgacure® 2959 initiator ina 5 mm diameter silicon tube. The constructs were cross-linked under UVlight (365 nm, 4-5 mW/cm²) to form a 5 mm tall cylinder. FF127 wascross-linked at a temperature of 4° C., 21° C. or 37° C. The wateruptake was evaluated by calculating the swelling ratio (Q_(M)), i.e.,the ratio of the wet weight (mass after swelling) divided by the dryweight (weight after lyophilization).

Biodegradation Measurements:

Biodegradation of the hydrogels was characterized by fluorometricallylabeling the biological component in the bio-synthetic hydrogel withamine-reactive N-hydroxysuccinimide-fluorescein (NHS-fluorescein). Therate of degradation was quantified by measuring the release of theprotein during the enzymatic dissolution of the hydrogel. 100 μlhydrogel plugs were stained overnight in a PBS solution containing 0.05mg/ml NHS-fluorescein, and washed extensively to remove unboundfluorescein. The plugs were then transferred into 3 ml of PBS with 0.01mg/ml trypsin and 0.1% sodium azide (Riedel-deHaen, India), andincubated at 37° C. with continuous agitation. Fluorescence measurementswere carried out in a Thermo Varioskan Spectrophotometer (excitationwavelength 494 nm, emission wavelength 518 nm) with Skanit2.2® Software.After the last time point, each hydrogel was hydrolytically dissociatedby adding 0.1 M NaOH. After 30 minutes, the emission values wererecorded at 100% degradation. Labeled hydrogel plugs without enzyme andunstained plugs with enzyme solution were used as negative controls.

Preparation of Cell-Seeded Constructs:

Cell-seeded hydrogel constructs were prepared by UV-inducedcross-linking of FF127 or FT1307 conjugates in solution in the presenceof dispersed human foreskin fibroblasts or HeLa cells. The passagedcells were trypsinized and suspended in 100 μl of a solution of theconjugate at a concentration of 10⁶ cells/ml, along with aphotoinitiator (0.1% w/v). The disc-shaped constructs were exposed to UVlight for 5 minutes at 4° C., 21° C. or 37° C. Control cell-seededconstructs were prepared from PEG (12 kDa)-fibrinogen, F127 poloxamerdiacrylate or T1307 tetraacrylate (3% w/w in PBS). The cell-seededconstructs were cultured for up to 6 days in Dulbecco's modified Eaglemedium (DMEM) containing 10% fetal bovine serum (FBS), 1%penicillin-streptomycin, 1% non essential amino acids, and 0.2%2-mercaptoethanol.

Light Microscopy and Fluorescent Microscopy:

Light microscopy and fluorescent microscopy were performed using anEclipse TE2000-S microscope (Nikon) or an Eclipse TS100 microscope(Nikon), and a digital camera.

Statistical Analysis:

Statistical analysis was performed using Microsoft Excel statisticalanalysis software. Data from independent experiments were quantified andanalyzed for each variable. Comparisons between two treatments were madeusing student's T-test (two tail, equal variance) and comparisonsbetween multiple treatments were made with analysis of variance (ANOVA).A p-value of <0.05 was considered to be statistically significant.

Example 1 F127 Poloxamer-Fibrinogen Conjugate

Fibrinogen was conjugated to F127 poloxamer-diacrylate (prepared asdescribed hereinabove, and as depicted in FIG. 1A) by a Michael-typeaddition reaction, as depicted in FIG. 1B. In order to compare theproperties of poloxamer-protein conjugates with those of poly(ethyleneglycol) (PEG)-protein conjugates, fibrinogen was conjugated with 12 kDaPEG-diacrylate (prepared as described hereinabove), using the samereaction.

A 3.5 mg/ml solution of fibrinogen in 150 mM phosphate buffer saline(PBS) with 8 M urea was supplemented with tris(2-carboxyethyl)phosphinehydrochloride (TCEP) at a molar ratio of 1.5:1 TCEP to fibrinogencysteine residues. PBS with 8 M urea and 280 mg/ml of the functionalizedpolymer (F127-DA or PEG-DA) was then added at a molar ratio of 4:1polymer molecules to fibrinogen cysteine residues. The mixture wasallowed to react for 3 hours at room temperature. The conjugated proteinwas then precipitated by adding 4 volumes of acetone. The precipitatewas redissolved in PBS containing 8 M urea at a protein concentration of10 mg/ml and then dialyzed against PBS for 2 days at 4° C., with the PBSbeing replaced twice per day. The dialysis tubing had a cutoff of12-14-kDa (Spectrum).

In order to establish total concentration of the F127-fibrinogen andPEG-fibrinogen conjugates, 0.5 ml of the conjugate solution waslyophilized for 24 hours and weighed. The net fibrinogen concentrationwas determined using a standard BCA™ Protein Assay (PierceBiotechnology) and the concentrations of the conjugates (dry weight) andfibrinogen were compared in order to determine the concentration ofsynthetic polymer in the conjugates. The efficiency of the conjugationreaction (ε_(conjugation)) was calculated based on the concentrationsand molecular weights of the synthetic polymer and fibrinogen, assuminga theoretical maximum of 29 synthetic polymer molecules per fibrinogenmolecule (as fibrinogen comprises 29 thiol groups), using the followingformula:

$ɛ_{conjugation} = {\frac{\left\lbrack {S.{Polymer}} \right\rbrack}{\lbrack{Fibrinogen}\rbrack} \times {theortical}\left\{ \frac{{MW}_{fibrinogen}}{29 \times {MW}_{S.{Polymer}}} \right\}}$

The mean fibrinogen concentration and conjugation efficiency obtainedfor 4 batches of each of F127-fibrinogen and PEG-fibrinogen conjugatesare summarized in Table 1.

TABLE 1 Mean fibrinogen concentration and conjugation efficiency ofsynthetic polymer-fibrinogen conjugates (mean ± standard error of themean) Synthetic Fibrinogen Conjugate polymer Conjugation concentrationconcentration concentration efficiency Synthetic MW (measured)(measured) (calculated) (ε_(conjugation)) polymer (kDa) (mg/ml) (mg/ml)(mg/ml) (%) F127-DA 12.6 7.7 ± 0.5  21 ± 2.3  13 ± 1.9  79 ± 8.4 PEG-DA12 8.9 ± 2   24.7 ± 6.7  15.8 ± 4.8  83.8 ± 10.5

As shown in Table 1, both F127 poloxamer and PEG were conjugated tofibrinogen with a relatively high conjugation efficiency. There was nostatistically significant difference between the conjugation efficiencyor fibrinogen concentration obtained with F127 poloxamer and PEG.

Example 2 Rheological Properties of F127 Poloxamer-Fibrinogen Conjugate(FF127) and Hydrogels Formed by Cross-Linking FF127

The rheological properties of the F127 poloxamer-fibrinogen conjugate(FF127) described in Example 1 was studied, as described in theMaterials and Methods section hereinabove.

As shown in FIG. 2, the shear storage modulus (G′) of FF127 increasedconsiderably at temperatures above about 20° C. The transition wasdependent on the concentration of FF127, as the storage modulus of 8mg/ml FF127 increased at a slightly lower temperature than did thestorage modulus of 4 mg/ml FF127.

As further shown in FIG. 2, the increase in the shear storage moduluswas accompanied by a peak in the shear loss modulus (G″) of the FF127.

As shown in FIG. 3A, the shear storage modulus was repeatedly increased(up to about 185 Pa) and decreased by raising the temperature to 37° C.and lowering the temperature to 15° C., indicating a reversibletransition.

These results indicates that FF127 undergoes a reverse thermal gelation(RTG) phase transition at such temperatures, as a result of theformation of a continuous polymeric matrix due to physical (i.e.,non-covalent) cross-linking of FF127 molecules, as depicted in FIG. 4.

It is notable that the reverse thermal gelation occurred atconcentrations of less than 20 mg/ml of conjugate (corresponding to afibrinogen concentration of approximately 8 mg/ml), as F127 does notexhibit reverse thermal gelation at concentrations less than 14.6% (w/w)[Cohn et al., Biomacromolecules 2005, 6:1168-1175].

Chemical (i.e., covalent) cross-linking of the FF127 molecules wasperformed by adding 0.1% (weight/volume) Irgacure® 2959 initiator toFF127 solutions, and irradiating the solution with UV light (365 nm, 4-5mW/cm²).

As shown in FIG. 5, chemical cross-linking of FF127 resulted in anirreversible increase in the storage modulus.

This result indicates that a hydrogel is formed due to UV-initiated freeradical polymerization of the acryl functional groups on the FF127molecules.

As shown in FIG. 6, the chemically cross-linked hydrogel exhibitedtemperature-dependent increases in the storage modulus and loss modulus.

As shown in FIG. 3B, the storage modulus of the chemically cross-linkedhydrogel was repeatedly increased (up to about 300 Pa) and decreased byraising the temperature to 37° C. and lowering the temperature to 15°C., indicating a reversible transition.

This result indicates that the chemically cross-linked hydrogel furtherexhibits RTG phase transitions due to physical cross-linking of FF127unimers, as observed in FF127 without chemical cross-linking.

As further shown in FIGS. 3A and 3B, the gelation of FF127 andchemically cross-linked FF127 at 37° C. was gradually eliminated in thepresence of collagenase (which degrades fibrinogen), in a dose-dependentmanner.

These results indicate that the reverse thermal gelation of both FF127and chemically cross-linked FF127 is associated with the molecularweight of the fibrinogen which forms the backbone of the FF127. As thefibrinogen was proteolytically degraded by the collagenase, the FF127unimers become smaller and the ability to form a physical polymericmatrix was thereby affected.

In order to explore the stability of the hydrogel network propertiesunder applied loading conditions, hydrogels were prepared from FF127 (8mg/ml) with or without chemical cross-linking and exposed to time-sweeprheological measurements as the applied shear stress levels wereincreased incrementally.

As shown in FIG. 7, the chemically cross-linked hydrogel was moreresponsive to temperature changes compared to the physical hydrogel,exhibiting a higher storage modulus at 37° C., but it collapsed underless oscillatory stress (70 Pa) than did the physical hydrogel (200 Pa).

As further shown therein, when the applied stress was removed at 37° C.,the chemically cross-linked hydrogel was restored almost completely,whereas the physically cross-linked hydrogel recovered only slightlyfrom the applied stress. However, lowering the temperature to 15° C. andraising it back to 37° C. completely restored the mechanical propertiesof both hydrogels.

These results indicate that the properties of the gels can be “reset” bylowering and raising the temperature.

Example 3 Effect of Cross-Linking Temperature on Physical Properties ofF127 Poloxamer-Fibrinogen Conjugate (FF127) Hydrogels

As the interactions between molecules of the FF127 conjugate aretemperature-dependent, it was hypothesized that the temperature duringthe chemical cross-linking reaction (T_(cl)) influences the chemicalcross-linking reaction. The chemical cross-linking of a hydrogel networkin the presence of free radicals may depend upon the mobility of themolecular precursors and their likelihood to form chemical cross-linkswhen undergoing a temperature-dependent physical transition.

Hydrogels were formed by UV-activated cross-linking, as described inExample 2, at different temperatures.

As shown in FIG. 8, the G′ value of the hydrogels at 37° C. wasinversely proportional to the temperature at which the UV-inducedcross-linking was performed. As further shown therein, the G′ values ofhydrogels chemically cross-linked at different temperatures were nearlyidentical at 15° C.

These results indicate that physical cross-linking has a highlysignificant effect on the physical properties which characterizechemically cross-linked networks, as the properties of the varioushydrogels varied considerably at 37° C., when physical cross-linking ispresent, but not at 15° C., when physical cross-linking is absent.

Example 4 Water Uptake by F127 Poloxamer Fibrinogen Conjugate (FF127)Hydrogels

Water uptake of cross-linked FF127 hydrogel constructs was determined asdescribed in the Materials and Methods section hereinabove. FF127 wascross-linked at a temperature of 21° C. or at a temperature of 37° C. Asa control, water uptake of cross-linked PEG (12 kDa)-fibrinogenhydrogels was determined as described hereinabove.

The water uptake in each hydrogel represents a characteristic measure ofits equilibrium state between water and polymeric matrix, and gives anindication of the structural forces involved in forming and sustainingthe hydrogel network. The swelling ratio (Q_(M)) was measured for thethree hydrogels at two separate ambient temperatures, 4° C. and 37° C.

As shown in FIG. 9, there was no significant difference in swellingratio between the different hydrogels at 4° C., whereas at 37° C., FF127and PEG-fibrinogen exhibit significantly different properties. FF127hydrogels expelled water when warmed to 37° C., whereas PEG-fibrinogenhydrogels did not.

As shown in FIGS. 9, 10A and 10B, FF127 cross-linked at 21° C. expelledmore water than did FF127 cross-linked at 37° C.

These results indicate that at a temperature at which reverse thermalgelation effects are negligible (e.g., 4° C.), the differentcross-linked polymers exhibit similar properties, whereas at atemperature at which reverse thermal gelation effects are significant(e.g., 37° C.), the degree of reverse thermal gelation affects theswelling properties of the polymer networks.

Example 5 Comparison of Biodegradation and Rheological Properties ofF127 Poloxamer-Fibrinogen Conjugate (FF127) Hydrogels

The biodegradation kinetics of chemically cross-linked FF127 and PEG (12kDa)-fibrinogen hydrogels were determined in a 0.01 mg/ml trypsinsolution at 37° C., as described hereinabove. FF127 hydrogels werecross-linked at temperatures of 21° C. and 37° C. were compared. Thehydrogels were cross-linked by exposure to UV, as described hereinabove.

The storage moduli of the hydrogels were determined as describedhereinabove. For comparison, a hydrogel was prepared by cross-linkingF127 diacrylate at 37° C. the storage modulus was determined

As shown in FIG. 11, there was a statistically significant differencebetween the three materials in terms of their biodegradation rate(p<0.05). The hydrogels made of PEG-fibrinogen degraded the fastest,with a half-life of 105±5 4 minutes, and were fully degraded after 24hours in 0.01 mg/ml trypsin. The hydrogels made of FF127 reached only˜60% degradation after 24 hours. The half-life of the FF127 hydrogelswas 420±66 minutes when cross-linked at 37° C., and 580±90 minutes whencross-linked at 21° C.

As shown in FIG. 12, the storage modulus of FF127 cross-linked at 37° C.was similar to that of the PEG-fibrinogen, and considerably lower thanthat of the FF127 cross-linked at 21° C. As further shown therein, thestorage modulus of FF127 cross-linked at 21° C. was similar to that ofF127 diacrylate cross-linked at 37° C.

Thus, although the biodegradation rate of cross-linked FF127 was lowerthan that of cross-linked PEG-fibrinogen, and was only moderatelyaffected by the cross-linking temperature, the storage modulus ofcross-linked FF127 was strongly affected by the cross-linkingtemperature.

These results indicate that factors determining biodegradation rate(e.g., type of polymer) can be selected relatively independently of thefactors determining rheological properties (e.g., cross-linkingtemperature).

Example 6 Tetronic® T1307-Fibrinogen Conjugate

Fibrinogen was conjugated to Tetronic® T1307 tetraacrylate (prepared asdescribed hereinabove) by a Michael-type addition reaction, usingessentially the same procedures as described in Example 1. As depictedin FIGS. 13A and 13B, conjugation of a tetraacrylate polymer tofibrinogen results in 3 free acrylate groups per conjugated polymer (1acrylate group attaches the fibrinogen to the polymer), providingincreased cross-linking ability.

The mean fibrinogen concentration and conjugation efficiency wasdetermined for 4 batches of T1307-fibrinogen, as described in Example 1.

The obtained solution of T1307-fibrinogen conjugate comprised 20.4±1.4mg/ml of the conjugate, 6.7±1 mg/ml fibrinogen, and 13.7±0.5 mg/mlsynthetic polymer. The conjugation efficiency was 66.3±8.5%.

Example 7 Physical Properties of T1307-Fibrinogen (FT1307) Hydrogels

The T1307-fibrinogen conjugate (FT1307) described in Example 6 waschemically cross-linked by UV light at a concentration of 6 mg/ml, attemperatures of 4° C., 21° C. or 37° C. Rheological properties, wateruptake and biodegradation of the obtained hydrogels were determined, asdescribed hereinabove.

As shown in FIGS. 14A and 14B, the cross-linking temperature of FT1307was inversely correlated to the storage modulus at 37° C.

As shown in FIG. 15, the cross-linking temperature of FT1307 wasinversely correlated to the amount of water expelled from the hydrogelwhen the hydrogel was warmed to 37° C. In contrast, the cross-linkingtemperature had little effect on the water uptake of the polymers at 4°C.

In contrast, as shown in FIG. 16, the cross-linking temperature ofFT1307 did not exhibit any clear correlation with the degradation ratesof the FT1307.

These results are similar to those presented in Examples 3 and 4, andindicate that the cross-linking temperature can be used to determine theproperties of polymer-protein hydrogels formed using a variety ofreverse thermal gelation polymers, and that the rheological propertiesof the hydrogels can be determined independently of the degradationrates.

Example 8 Cell-Seeded F127-Fibrinogen (FF127) Hydrogels

Cell-seeded hydrogel constructs were prepared by UV-inducedcross-linking of a FF127 conjugate solution in the presence of dispersedhuman foreskin fibroblasts (Lonza, Walkersville, Md., USA), as describedin the Materials and Methods section. Control cell-seeded constructswere prepared from PEG (12 kDa)-fibrinogen and F127 poloxamerdiacrylate. Samples for histology were fixed in 4% formalin on day 3 andon day 6 of each experiment. Cross-sections were stained withhematoxylin and eosin (H & E) for imaging.

As shown in FIG. 17, the formation of lamellipodia and a spindledcellular morphology proceeded more rapidly in FF127 cross-linked at 37°C. than in FF127 cross-linked at 21° C. On day 3, the cells in FF127cross-linked at 21° C. were relatively rounded and had only begun toform lamellipodia, whereas in the FF127 cross-linked at 37° C., thecells were highly spindled with many cellular lamellipodia. Accordingly,on day 6, the cells in FF127 cross-linked at 21° C. had begun to invadethe matrix through cellular lamellipodia, but only a few were fullyspindled, whereas most of the cells in FF127 cross-linked at 37° C. werefully spindled and exhibited many lamellipodia.

As further shown therein, in the cross-linked PEG-fibrinogen, which ischaracterized both by a relatively high biodegradability and low storagemodulus (as shown hereinabove), cells were highly spindled by day 3.

As further shown therein, in cross-linked F127 diacrylate, which lacksfibrinogen, cells remained completely rounded and did not form cellularextensions.

Cell-seeded FF127 hydrogel constructs were also prepared by physicalcross-linking at 37° C. without chemical cross-linking by UV light. Thecells in such hydrogels were compared to those in FF127 hydrogelconstructs chemically cross-linked at 37° C.

As shown in FIG. 18, cells in FF127 hydrogels with only physicalcross-linking and cells in FF127 hydrogels with both physical andchemical cross-linking both displayed a similar morphology. On day 3 inboth materials, the cells exhibited spindled morphology with protrusionsinvading the matrix, and on day 6 in both materials, the cells werefully spread and highly spindled.

The viability of the encapsulated cells was determined on day 0 and onday 3 of each experiment. The cells were removed from the construct bydissolving the fibrinogen in 0.4 mg/ml collagenase 1A solution for 4hours followed by 5 minutes centrifugation (1000 rotations per minute).The pellet was redissolved in 100 μl of staining solution containing0.004 mM ethidium homodimer-1 and 2 mg/ml Hoechst 33342 in PBS. Thecells were stained for 30 minutes on an orbital shaker in the dark andthen centrifuged for 5 minutes (1000 rotations per minute). The cellpellet was dissolved in 25 μl of PBS, and imaged on a glass microscopeslide overlaid with a cover slip. The stained cells were imaged byfluorescent microscopy. The live and dead cells were counted andnormalized by a control suspension that was not exposed to UV light.

As shown in FIG. 19, the viability of cells in chemically cross-linkedFF127 was at least 88% on day 0 and at least 85% on day 3. The cellviability on both days was higher in FF127 cross-linked at 37° C. thanin FF127 cross-linked at 21° C., although the differences were notstatistically significant.

The above results indicate that hydrogels formed frompoloxamer-fibrinogen conjugates, including hydrogels with and withoutchemical cross-linking of the conjugates, can serve as matrices for cellgrowth and invasion. The results further indicate that the rate of cellinvasion can be modulated by selecting the physical properties of thegel, for example, by selecting a suitable cross-linking temperature.

Example 9 Cellular Outgrowth into F127-Fibrinogen (FF127) Hydrogels

Outgrowth experiments were performed using a dense tissue construct madefrom compacted bovine aortic smooth muscle cells (Genlantis) seeded incollagen gels. Each compacted cell-seeded collagen gel was encapsulatedinside an FF127 hydrogel. As a control, a compacted cell-seeded collagengel was encapsulated inside a PEG-fibrinogen hydrogel.

The collagen-based tissue was made from a solution of 5×DMEM, 10% fetalbovine serum, reconstituted collagen type-I solution in 0.02 N aceticacid (2 mg/ml), and 1 M NaOH with smooth muscle cells dispersed at aconcentration of 3×10⁶ cells/ml. The cell-seeded collagen gels werecultured for 2 days in culture medium before the compacted tissue wasplaced in 300 μl of FF127 (or PEG-fibrinogen) conjugate solution andphotoinitiator in a 48-well plate. After exposure to 5 minutes of UVlight at 37° C. or 21° C., the encapsulated tissue was cultured insidethe hydrogel with 500 μl of culture medium. The cellular outgrowth fromthe collagen gel into the FF127 (or PEG-fibrinogen) encapsulating matrixwas monitored daily for up to 5 days. The outgrowth results werequantified by measuring the average travel distance of the cells fromthe margins of the dense collagen tissue into the FF127 (orPEG-fibrinogen) hydrogel using phase contrast micrographs of the samplestaken at set time intervals.

As shown in FIGS. 20A and 20B, in each of the three tested materials(FF127 cross-linked at 21° C. and at 37° C., and cross-linkedPEG-fibrinogen), the cells began to invade the matrix surrounding thetissue mass after 1 day and continued to invade the matrix for theduration of the experiment.

As shown in FIG. 20B, the rate of invasion in the FF127 cross-linked at37° C. remained constant for the duration of the experiment, whereas therate of invasion decreased in the FF127 cross-linked at 21° C. and inthe PEG-fibrinogen, starting on the third day of the experiment.Beginning from day 3, there was a statistically significant differencebetween the cell migration distance in FF127 cross-linked at 21° C. andin FF127 cross-linked at 37° C. On day 4, the distance the cellstraveled was 21% lower in FF127 cross-linked at 21° C. than in FF127cross-linked at 37° C., and on day 5, the distance was 11% lower inFF127 cross-linked at 21° C. The invading cells did not exhibit amorphological difference among the three materials tested.

These results further indicate that the rate of cell invasion can bemodulated by selecting the physical properties of the gel.

Example 10 Cell-Seeded T1307-Fibrinofen (FT1307) Hydrogels

Cell-seeded hydrogel constructs were prepared by UV-inducedcross-linking of a FT1307 conjugate solution in the presence of humanforeskin fibroblasts and HeLa human adenocarcinoma cells, as describedin the Materials and Methods section. Control cell-seeded constructswere prepared from T1307 tetraacrylate.

In order to view the seeded cells and determine their viability, thecell-seeded constructs were placed in a well holding 2 ml of 4 mMcalcein AM and 2 mM ethidium homodimer-1 in DMSO, and incubated for 45minutes. Viable cells are stained by calcein and non-viable cells arestained by ethidium. Each construct was then washed twice for 15 minutesin PBS in order to remove excess dye molecules. The cells were thenimaged by fluorescent microscopy.

As shown in FIG. 21, cell spreading of fibroblasts proceeded relativelyrapidly in FT1307 cross-linked at 37° C., and more slowly in FT1307cross-linked at 21° C., and was almost completely halted in FT1307cross-linked at 4° C. The rate of cell spreading was inverselycorrelated to the storage modulus, which was 52 Pa, 244 Pa and 373 Pafollowing cross-linking temperatures of 37° C., 21° C. and 4° C.,respectively.

As further shown in FIG. 21, cell viability was high in all three typesof FT1307 matrices, as evidenced by the paucity of ethidium(orange-colored) staining.

As shown in FIG. 22, HeLa cell colonies were relatively dense andconfined in FT1307 cross-linked at 4° C., somewhat less dense andconfined in FT1307 cross-linked at 21° C., and relatively disperse inFT1307 cross-linked at 37° C.

The above results indicate that the rate of cell spreading and thestructure of cell colonies is affected by the physical properties of thematrix, which can be determined by cross-linking temperature.

Example 11 Cellular Outgrowth in F127-Fibrinogen (FF127) HydrogelsEncapsulated within T1307-Fibrinofen (FT1307) Hydrogels

Outgrowth experiments were performed using FF127 physically cross-linkedcapsules containing cultures or co-cultures of human dermal fibroblastsand HeLa cells, which were entrapped in FT1307 chemically cross-linkedhydrogels. Trypsinized cells were suspended in 500 μl of FF127 conjugatesolution at a concentration of 10⁷ cells/ml, and loaded into aMicro-Fine™ 30 G syringe (BD, New Jersey, USA).

As shown in FIG. 23A, while keeping the temperature below 20° C., drops20 of the suspension of cells in FF127 were added from syringe 10 into agently stirred phosphate buffered saline (PBS) medium 30 kept at atemperature of 37° C. The drops 20 gelled upon exposure to a temperatureof 37° C. in PBS medium 30, forming cell-seeded capsules 40. Thecell-seeded capsules 40 were isolated and incubated in DMEM cell culturemedium for 2 days at 37° C., and then seeded in 300 μl of FT1307conjugate solution with a photoinitiator (0.1% w/v), and exposed to UVlight for 5 minutes at temperatures of 37° C., 21° C. or 4° C.

As shown in FIG. 23B, this procedure resulted in a co-polymericconstruct—so as to entrap the relatively soft physically cross-linkedFF127 capsules 50 within a harder chemically cross-linked FT1307 milieu60.

As described hereinabove, cross-linking temperatures of 37° C., 21° C.or 4° C. resulted in FT1307 storage moduli of 52 Pa, 244 Pa and 373 Pa,respectively.

As shown in FIGS. 24A and 24B, fibroblasts exhibited outgrowths in ahydrogel with a low storage modulus (52 Pa), but not in a hydrogel witha high storage modulus (373 Pa).

In comparison, as shown in FIGS. 25A and 25B, HeLa cells exhibiteddifferent migration/invasion strategies in hydrogels with differentmoduli; the cells exhibited individual amoeboid migration in a hydrogelwith a low storage modulus (52 Pa), and collective multicellularmigration in a hydrogel with a high storage modulus (373 Pa).

Co-cultures of HeLa cells and fibroblasts were seeded in FF127 capsuleswithin FT1307 hydrogels in order to assess how the hydrogel modulusaffects the development of heterogenic cultures. In order todifferentiate between the fibroblasts and HeLa cells, GFP (greenfluorescent protein)-labeled fibroblasts and DiI(1,1′-dioctadecyl-3,3,3′3′-tetramethylindocarbocyanineperchlorate)-stained HeLa cells were co-cultured.

As shown in FIGS. 26A and 26B, in an FT1307 hydrogel with a high storagemodulus (373 Pa), HeLa cells pushed into the FT1307 hydrogel, increasingthe diameter of the capsule, whereas fibroblast outgrowth was halted.

As shown in FIGS. 27A and 27B, in an FT1307 hydrogel with a low storagemodulus (52 Pa), the capsule front was dominated by fibroblasts, whicheffectively performed mesenchymal migration into the FT1307 hydrogel.

The above results indicate that the outgrowth of cells from homogeneousand heterogeneous cultures can be modulated according to the physicalproperties of a surrounding hydrogel.

The above results further indicate that heterogeneous hydrogels can beprepared from more than one type of polymer-protein conjugate.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

What is claimed is:
 1. A conjugate comprising a polypeptide havingattached thereto at least two polymeric moieties, at least one of saidpolymeric moieties exhibiting a reverse thermal gelation.
 2. Theconjugate of claim 1, wherein each of said polymeric moieties exhibits areverse thermal gelation.
 3. The conjugate of claim 1, wherein saidpolypeptide comprises a fibrinogen or a fragment thereof.
 4. Theconjugate of claim 1, wherein at least one of said polymeric moietiescomprises a poloxamer (poly(ethylene oxide-propylene oxide) copolymer).5. A composition-of-matter comprising a cross-linked form of theconjugate of claim 1, said cross-linked form comprising a plurality ofmolecules of the conjugate cross-linked to one another.
 6. Thecomposition-of-matter of claim 5, being a hydrogel.
 7. Thecomposition-of-matter of claim 5, generated by a reverse thermalgelation of said plurality of molecules of the conjugate in an aqueoussolution.
 8. The composition-of-matter of claim 5, wherein saidplurality of molecules of the conjugate are non-covalently cross-linkedto one another.
 9. The composition-of-matter of claim 5, wherein atleast one of said polymeric moieties further comprises a cross-linkingmoiety, and said plurality of molecules of the conjugate are covalentlycross-linked to one another.
 10. The composition-of-matter of claim 5,further comprising cells therein.
 11. The composition-of-matter of claim5, further comprising growth factors.
 12. A process of producing thecomposition-of-matter of claim 5, the process comprising heating asolution of a plurality of molecules of a conjugate comprising apolypeptide having attached thereto at least two polymeric moieties, atleast one of said polymeric moieties exhibiting a reverse thermalgelation, from a first temperature to a second temperature, said secondtemperature being such that a reverse thermal gelation of the conjugatein said solution is effected, thereby producing thecomposition-of-matter.
 13. The process of claim 12, wherein saidcomposition-of-matter is produced in vivo.
 14. The process of claim 13,wherein said solution further comprises cells derived from an autologoussource.
 15. A process of producing the composition-of-matter of claim 9,the process comprising subjecting a solution comprising a plurality ofmolecules of a conjugate comprising a polypeptide having attachedthereto at least two polymeric moieties, at least one of said polymericmoieties exhibiting a reverse thermal gelation, at least one of saidpolymeric moieties further comprising at least one cross-linking moietyfor covalently cross-linking a plurality of molecules of the conjugateto one another, to conditions that effect covalent cross-linking of saidcross-linking moieties, thereby producing the composition-of-matter. 16.The process of claim 15, wherein said covalent cross-linking is effectedin vivo.
 17. The process of claim 16, wherein said solution furthercomprises cells derived from an autologous source.
 18. A process ofproducing the composition-of-matter of claim 9 in vivo, the processcomprising: (a) subjecting a solution comprising a plurality ofmolecules of a conjugate comprising a polypeptide having attachedthereto at least two polymeric moieties, at least one of said polymericmoieties exhibiting a reverse thermal gelation, at least one of saidpolymeric moieties further comprising at least one cross-linking moietyfor covalently cross-linking a plurality of molecules of the conjugateto one another, to conditions that effect covalent cross-linking exvivo, to thereby produce a covalently cross-linked scaffold; and (b)subjecting said covalently cross-linked scaffold to a physiologicaltemperature in vivo, such that a reverse thermal gelation of saidscaffold is effected in vivo, thereby producing thecomposition-of-matter.
 19. The process of claim 18, wherein saidsolution further comprises cells derived from an autologous source. 20.A method of inducing formation of a tissue in vivo, the methodcomprising implanting the composition-of-matter of claim 5 in a subject,to thereby induce the formation of the tissue.
 21. The method of claim20, wherein said composition-of-matter further comprises cells derivedfrom said subject.
 22. The method of claim 20, wherein saidcomposition-of-matter further comprises growth factors.
 23. The methodof claim 20, wherein said tissue is cartilage.
 24. A method of inducingformation of a tissue in vivo, the method comprising implanting aplurality of molecules of the conjugate of claim 1 in a subject, tothereby induce the formation of the tissue.
 25. The method of claim 24,further comprising implanting in said subject cells derived from saidsubject in combination with said plurality of molecules of theconjugate.
 26. The method of claim 24, wherein said tissue is cartilage.27. A method of treating a subject having a disorder characterized bytissue damage or loss, the method comprising implanting thecomposition-of-matter of claim 5 in a subject, to thereby induceformation of said tissue, thereby treating the disorder characterized bytissue damage or loss.
 28. The method of claim 27, wherein saidcomposition-of-matter further comprises cells derived from said subject.29. The method of claim 27, wherein said composition-of-matter furthercomprises growth factors.
 30. The method of claim 27, wherein saiddisorder is an articular cartilage defect.
 31. A method of treating asubject having a disorder characterized by tissue damage or loss, themethod comprising implanting a plurality of molecules of the conjugateof claim 1 in a subject, to thereby induce formation of said tissue,thereby treating the disorder characterized by tissue damage or loss.32. The method of claim 31, further comprising implanting in saidsubject cells derived from said subject in combination with saidplurality of molecules of the conjugate.
 33. The method of claim 31,wherein said disorder is an articular cartilage defect.